Tenant Stats endpoint

[pdeziel]

Scope of changes

This adds an initial statistics endpoint for Tenant which for now displays counts of projects, topics, and apikeys in a tenant. The goal of this is to support some visual components on the Beacon UI when the user is viewing a tenant.

Fixes SC-13298

Type of change

• new feature
• bug fix
• documentation
• testing
• technical debt
• other (describe)

Acceptance criteria

The endpoint URL makes sense and the test coverage is sufficient.

Author checklist

• I have manually tested the change and/or added automation in the form of unit tests or integration tests
• I have updated the dependencies list
• I have recompiled and included new protocol buffers to reflect changes I made
• I have added new test fixtures as needed to support added tests
• Check this box if a reviewer can merge this pull request after approval (leave it unchecked if you want to do it yourself)
• I have moved the associated Shortcut story to "Ready for Review"

Reviewer(s) checklist

• Any new user-facing content that has been added for this PR has been QA'ed to ensure correct grammar, spelling, and understandability.
• Are there any TODOs in this PR that should be turned into stories?

[shortcut-integration]

This pull request has been linked to Shortcut Story #13298: Tenant API: add Tenant quick view Statistic data endpoint.

[pdamodaran]

Looks good - the tests are quite extensive. Nice work!