[receiver/azuremonitorreceiver] feat: multi subscriptions support and automatic discovery

[celian-garcia]

Component(s)

receiver/azuremonitor

Is your feature request related to a problem? Please describe.

When a tenant contains multiple subscriptions, if a new one is created you have to create a new receiver.

Describe the solution you'd like

I want to be able to say "take all the subscriptions of the tenant"

Describe alternatives you've considered

Maintaining a config but too painful.

Additional context

For an additional context, I'd like to create a new PR after that to revive the topic of the batch api usage. #29593

The idea is that if you have many subscription with many resources, you can be rate limited by Azure with the current get of Resource metrics. Using the batch API, you don't have anymore the problems of rate limitation. We're using already it from a fork in Amadeus for 1 year and it's promising.

[github-actions]

Pinging code owners:

• receiver/azuremonitor: @nslaughter @codeboten

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