* Add Usage Details API with patches

This is a stripped down version of the 2019-10-01 version of Usage
Details API and Forecasts API with small changes required to data
range data filtering.

The standard version of the API does non support the required date
filtering required to handle MCA customers.

I hope in the future Microsoft will release a new version of this API
with support for MCA, so we can get rid of this code and just use the
upstream version.

* Update billing module to use API 2019-10-01

Usage Details is now using API version 2019-10-01, and now the module
can handle both the legacy and modern data formats.

Due to restrictions for modern customers with a Microsoft Customer
Agreement [1], the start and end dates are passed to the `List()`
method in both the `$filter` and `start/endDate` query string
parameters.

[1]: https://docs.microsoft.com/en-us/azure/cost-management-billing/costs/manage-automation#get-usage-details-for-a-scope-during-specific-date-range

* Fix linter objections

* Fix tests

* Fix all linter complaints

* Switch to forked github.com/Azure/azure-sdk-for-go

We created a fork [1] of the stream github.com/Azure/azure-sdk-for-go
with the patches needed to run Usage Details API with modern Azure
accounts.

[1]: https://github.com/elastic/azure-sdk-for-go

* Add logger

* Properly initialize shared event fields

* Remove the embedded azure clients

We no longer need this proof-of-concept code; we are going to leverage
the external fork [1].

[1]: https://github.com/elastic/azure-sdk-for-go

* I will run the linter before committing, I will...

* Do not fail on unsupported subscriptions

Forecasts API 2019-10-01 supports Enterprise customers only [1], so it
returns a 404 error when used by MCA customers.

Check for 404s and log a warning, so at least the Usage Details are
successfully collected and sent to Elasticsearch.

[1]: "Provides operations to get usage forecasts for Enterprise
Subscriptions"; see https://docs.microsoft.com/en-us/rest/api/consumption/
fore more.

* Extract resource name from path for modern data

The resource name is not available as a standalone field, but can
be extracted from the instance name field.

* Fix linter objections and failing tests

* Update Go mod/sum

* Finalize the list of supported fields

* Cleanup

* Update generated docs

* Remove duplicated field

* Update generated docs (yes, again)

* Fix typos and leftovers

* Go.mod replace: use version instead of ts+hash

It's better looking and more meaningful

* Use spaces as logger name separator

Other logger names in the azure package are using this convention.

* Fix a HUGE mistake in start time and add a comment

* Switch to structured logging

* Handle unsupported data format as an error

* Remove unclear detail

We'll add it back when we can explain the context.

* Move time window calculation to a testable func

Now it's asier to read and test.

* Add missing file header

* Update x-pack/metricbeat/module/azure/billing/billing_test.go

Co-authored-by: kaiyan-sheng <kaiyan.sheng@elastic.co>

* Update CHANGELOG

* Fix typo in a function name

Co-authored-by: kaiyan-sheng <kaiyan.sheng@elastic.co>
Co-authored-by: tommyers-elastic <106530686+tommyers-elastic@users.noreply.github.com>
(cherry picked from commit 1f232dc)

Preallocating events slice using the number of usage details as
starting size.