Implement Azure resource fetching in the Discovery service

[mvbrock]

Part of of https://github.com/gravitational/access-graph/issues/640 to implement Azure resource fetching in the Discovery service, and originating from the Azure integration POC branch master...mvbrock/azure-integration-poc. This PR is dependent on #48628 which specifies the gRPC messages/methods for transmitting Azure resources to the Access Graph. A new Azure fetcher is introduced alongside the AWS fetcher, as well as the addition of Azure role definition/assignment clients in the Cloud library, per https://github.com/gravitational/access-graph/issues/1314.

[public-teleport-github-review-bot]

@mvbrock - this PR will require admin approval to merge due to its size. Consider breaking it up into a series smaller changes.

[hugoShaka]

This PR is quite large. This make reviewing hard, as reviewers we are more likely to miss bugs, and this makes reverting/backporting your PR harder because of the conflicts and potential protobuf breaking changes.

Working on a single branch to get the full thing working is positive as this avoids having to backtrack and fix things we forgot on a previous PR. However it might be useful to split the resulting changeset into smaller PRs. You will get a higher quality review and it will take less time to get merged.

Teleporters tend to split the PR into at least:

• one PR with the protobuf/generated content
• one PR with the client part
• one PR with the service/cache collection part
• one or more PR adding the new logic, services, ... (e.g. the new fetchers in the discovery service)

This does not apply to every PR but as a rule of thumb, splitting large PRs into smaller chunks is a best practice and you might want to consider breaking PRs larger than 500 locs.

[marcoandredinis]

We can leave it as is 👍
I still think we should converge on a single way of setting discovery matchers, and it should use, IMO, the DiscoveryConfig resource.
However, for the sake of consistency, let's have it in both places.

[mvbrock]

Closing this PR since split PRs have been created and listed below. Copied a few remaining comments here from @marcoandredinis into those PRs as well.

• Protobuf and configuration for Access Graph Azure Discovery #50364
• Adding the Azure sync module functions along with new cloud client functionality #50366
• Adding Azure sync functionality which can be used by the Azure Fetcher #50367
• Invoking the Azure fetcher in the Discovery service #50369