feat: POC of adding subscription_name to metric labels

[jiping-s]

This is a proof of concept for adding subscription_name (1:1 to subscription_id) for metrics. I don't have time to complete it for all the requirements, but if anyone is interested please take it over.

Applies to both of azure metrics and promitor's internal metrics.

• Verified manually with Prometheus sink; No other sink tested and no unit tests
• Works for resources discovered by ResourceDiscovery only

How it works:

• A new API endpoint in ResourceDiscovery to expose list of subscription ID -> name
• The API is queried in scraper in the same schedule jobs for azure metrics. ID->Name is only added or updated, never deleted.
• In scraper, AzureScrapingSystemMetricsPublisher adds associated subscription_name if there is a subscription_id label <- for promitor's internal metrics
• In scraper, MetricSinkWriter adds associated subscription_name if there is a subscription_id label <- for azure metrics

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

:white_check_mark: tomkerkhove
:x: jiping-s
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[tomkerkhove]

Thank you! I'll review it asap

[tomkerkhove]

This is for https://github.com/tomkerkhove/promitor/issues/1665 I presume?