Add stream-compatible variant of Kratos validation middleware

[wscalf]

PR Template:

Describe your changes

• Similar to the logging PR, this adds a variant of the validation that's compatible with streaming endpoints. However, like the Kratos middleware, it only calls the generated Validate method on the request, which doesn't consistently call the Validate method on embedded messages. See: https://github.com/project-kessel/relations-api/blob/main/api/relations/v0/lookup.pb.validate.go#L53 (it calls Validate on the pagination field, but not the other embedded messages.)

This issue covers that: https://issues.redhat.com/browse/RHCLOUD-33724

Ticket reference (if applicable)

Fixes # RHCLOUD-33932

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?

[akoserwal]

go-kratos/kratos#3359 (comment)