Describe the feature:

Blocked by #243932

When we will finish with the support of promql at the AST we will be able to move on with supporting it at the editor. The PROMQL is a source command.

• Highlighting should get updated
• Client side validation
• Autocomplete

We don't need to be very thorough as we are with the rest of ES|QL but we need to be sure that at least:

• don't complain for things we should not
• autocomplete to work decently (for example now if you use PROMQL it suggests FROM afterwards)

https://github.com/elastic/metrics-program/blob/main/docs/promql/esql-promql-syntax.md

This works like all source commands (meaning that the output can be the input for other processing commands

Milestone 0

• PROMQL appears in command suggestions at query start
• After typing PROMQL , parameter suggestions appear
• After typing PROMQL index=, timeseries indices are suggested
• After typing PROMQL step=, duration values are suggested (and so on..)
• Parameters already used are not suggested again
• Fix paths after queries (eg. suggest pipes in All forms that we can present a PROMQL query)
• Add support for multi Index
• Tests pass for all autocomplete scenarios
• Column After
• Local Validation for params

Requires PR to our external package:

• Add PROMQL to tokenizer keyword list.

Milestone 1 - Basic Query Support

• Add Promql Signatures support
• Function names and aggregation (rate, sum, avg ....`)
• Aggregation modifiers (by, without) (e.g sum(rate...) by(label ))
• Metric and labels
• operators ( ⚠️ Although we have implemented all operators, we only show the arithmetic ones for now. ES needs to end support for comparators and logic.)
• Position detection inside (query) vs after
• Show all timeseries metrics by default
• Pass breackdown, metrics to the pipe
• Local Validation for queries

Milestone 1.1 - Selectors & Labels

• Group labels inside by(...)
• Label suggestion ----> hidden until I complete the task below
• Label matcher (=, !=, =~, !~) after label name
• Range duration inside [] (5m, 1h, 1d) (we use a free placeholder)

Milestone 1.2 - Aggregations & Advanced

• Alternative way to call aggregation modifiers (by, without) eg. like sum by(..) (...) ....) .
• ⚠️ Without aggregator ---> (No supported yet by ES)
• ⚠️ Binary modifiers (on, ignoring, group_left, group_right) ---> (No supported yet by ES)
• ⚠️ offset ---> (No supported yet by ES)
• ⚠️ @ modifier---> (No supported yet by ES)
• ⚠️Subquery resolution ([5m:1m] ) ---> (Probably we don't need it)

Other (not urgent)

• Handling comma for list of selectors
• Documentation
• Signature Popup
• Hover

Post milestones

• Add buckets parameter
• Add scrape interval