3505: Csv delimiter r=irevoire a=irevoire

Fixes #3442
Closes #2803
Specified in meilisearch/specifications#221

This PR is a reimplementation of #2803, on the new engine. Thanks for your idea and initial PR `@MixusMinimax;` sorry I couldn’t update/merge your PR. Way too many changes happened on the engine in the meantime.

**Attention to reviewer**; I had to update deserr to implement the support of deserializing `char`s

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It introduces four new error messages;
- Invalid value in parameter csvDelimiter: expected a string of one character, but found an empty string
- Invalid value in parameter csvDelimiter: expected a string of one character, but found the following string of 5 characters: doggo
- csv delimiter must be an ascii character. Found: 🍰 
- The Content-Type application/json does not support the use of a csv delimiter. The csv delimiter can only be used with the Content-Type text/csv.

And one error code;
- `invalid_index_csv_delimiter`

The `invalid_content_type` error code is now also used when we encounter the `csvDelimiter` query parameter with a non-csv content type.

Co-authored-by: Tamo <tamo@meilisearch.com>

* Bump API version

* Metrics API — Introduce a `/metrics` route for observability / monitoring purposes (#174)

* init spec for /metrics

* Rename spec filename and add description for metrics

* update metrics name and type col in the metrics table; add auth errors

* Add --enable-metrics-route to instance-options.md specification

* Precise metrics

* update open-api.yml

* Add telemetry instance property

* Mention metrics route on stats.get action

* Add  action

* Precise  action description

* Rephrase future possibility

* Add MEILI_ENABLE_METRICS_ROUTE

* rename all the cli parameter to the experimental variant

* Update text/0174-metrics-api.md

Co-authored-by: Guillaume Mourier <guillaume@meilisearch.com>

* Update open-api.yaml

Co-authored-by: Guillaume Mourier <guillaume@meilisearch.com>

* Update text/0085-api-keys.md

Co-authored-by: Guillaume Mourier <guillaume@meilisearch.com>

* Apply suggestions from code review

Co-authored-by: Tamo <tamo@meilisearch.com>

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Co-authored-by: Tamo <tamo@meilisearch.com>

* API Keys - Introduce `*` wildcard char at the last position to express access to multiple indexes starting with the same string (#189)

* Bump open-api spec

* Precise that the * wildcard char can be used at the last position to match multiple indexes starting with the same string

* Update future possibilities

* Update the index wildcard pattern error message

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Co-authored-by: Clément Renault <clement@meilisearch.com>

* Documents API — Support a csv delimiter customization (#221)

* specify the support of the csv-delimiter

* Apply suggestions from code review

* get rid of the last 'future possibility' that is being described in this PR

* Update openAPI specification

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Co-authored-by: Guillaume Mourier <guillaume@meilisearch.com>

* Update the geo-search spec to mention the fact that null is a valid geo field (#222)

* GeoSearch — Add the `_geoBoundingBox` built-in filter (#223)

* Add geoBoundingBox built-in filter description

* Add missing parts

* Update text/0059-geo-search.md

Co-authored-by: Tamo <tamo@meilisearch.com>

* Replace the top left / bottom right signature to a top right / bottom left signature

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Co-authored-by: Tamo <tamo@meilisearch.com>

* Search API — Add `facetStats` description (#224)

* update search-api.md

* rephrase

* update open-api.yml

* rephrase, add example on open-api.yml

* Add examples

* fix

* Update text/0118-search-api.md

Co-authored-by: Louis Dureuil <louis.dureuil@gmail.com>

* rephrase

* Clarify that facet stats are for all search results

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Co-authored-by: Louis Dureuil <louis.dureuil@gmail.com>

* Multi Search API (#225)

* Add multi-search spec

* Change possible HTTP return codes for index_not_found

* Add multi-search to openAPI

* Update telemetry

* openAPI: shorter summary for multi-search

* openAPI: attempt to remove superfluous "values" field in multisearch request/response

* Apply review suggestions for openAPI

Co-authored-by: Guillaume Mourier <guillaume@meilisearch.com>

* Apply review suggestions for multi search API

Co-authored-by: Guillaume Mourier <guillaume@meilisearch.com>

* Add queries/results keys to openAPI examples

Co-authored-by: Guillaume Mourier <guillaume@meilisearch.com>

* fix indent

* Apply review suggestions for multi search API

Co-authored-by: cvermand <33010418+bidoubiwa@users.noreply.github.com>

* OpenAPI: Change summary to `Multi Search`

* use backticks instead of ticks in multi search API example

* Apply review suggestions for multi search API

Co-authored-by: Maryam <90181761+maryamsulemani97@users.noreply.github.com>

* remove superfluous newline from telemetry file

Co-authored-by: Guillaume Mourier <guillaume@meilisearch.com>

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Co-authored-by: Guillaume Mourier <guillaume@meilisearch.com>
Co-authored-by: cvermand <33010418+bidoubiwa@users.noreply.github.com>
Co-authored-by: Maryam <90181761+maryamsulemani97@users.noreply.github.com>

* Add small blurb on index count / max size (#226)

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Co-authored-by: Tamo <tamo@meilisearch.com>
Co-authored-by: Clément Renault <clement@meilisearch.com>
Co-authored-by: Louis Dureuil <louis.dureuil@gmail.com>
Co-authored-by: cvermand <33010418+bidoubiwa@users.noreply.github.com>
Co-authored-by: Maryam <90181761+maryamsulemani97@users.noreply.github.com>