[DRAFT] RHCLOUD-43569: Indicative PR for merging inventory-api and relations-api

[merlante]

PR Template:

Describe your changes

• Merged ZanzibarRepository interface from relations-api with Authorizer interface from inventory-api to form the new common interface between inventory and the relations repository, preferring ZanzibarRepository naming and relations-domain typed arguments.
• Removed kessel authorizer implementation from inventory-api and replace with SpiceDbRepository ZanzibarRepository implementation from relations-api, which implements the new interface.
• Replaced kessel authorizer config with spicedb repository config, effectively removing an unnecessary layer of abstraction.
• Dispensed with the relations-api proto specification, but retained many of the relations-domain structs, which are now simply domain objects.
• SpiceDb becomes a configurable and switchable dependency of inventory-api.
• SpiceDbRepository ported over with minimal (i.e. cosmetic) changes. [TODO: double check this with cross repo diff]
• SpiceDbRepository integration tests (i.e. repository tests against a spicedb test container) ported over to inventory-api provide a strong regression test for this layer (along with the testcontainer code).
• Only the minimal changes to accomplish the above and fix the tests were made.

Next steps/not yet done:

1. Refactor the "Authorizer" and associated files to be a "repository" in internal/data alongside resourcerepository, etc. This should be very straightforward, except that there is already a legacy relationshiprepository that is kind of "in the way".

Ticket reference (if applicable)

Fixes #RHCLOUD-43569

Checklist

• Are the agreed upon acceptance criteria fulfilled?

• Was the 4-eye-principle applied? (async PR review, pairing, ensembling)

• Do your changes have passing automated tests and sufficient observability?

• Are the work steps you introduced repeatable by others, either through automation or documentation?

  • If automation is possible but not done due to other constraints, a ticket to the tech debt sprint is added
  • An SOP (Standard Operating Procedure) was created

• The Changes were automatically built, tested, and - if needed, behind a feature flag - deployed to our production environment. (Please check this when the new deployment is done and you could verify it.)

• Are the agreed upon coding/architectural practices applied?

• Are security needs fullfilled? (e.g. no internal URL)

• Is the corresponding Ticket in the right state? (should be on "review" now, put to done when this change made it to production)

• For changes to the public API / code dependencies: Was the whole team (or a sufficient amount of ppl) able to review?

[app-sre-bot]

Can one of the admins verify this patch?

[sourcery-ai]

Sorry @merlante, your pull request is larger than the review limit of 150000 diff characters