[VTAdmin] Output warning log if cluster ID has invalid characters

[notfelineit]

Description

In VTAdmin, Cluster IDs are used as part of the gRPC resolver name. As such, they need to follow a specific URI scheme, as specified in https://datatracker.ietf.org/doc/html/rfc3986#section-3.1

Namely, Cluster IDs can only have alphanumeric characters, a +, ., or - and nothing else.

The first step of Cluster ID validation is simply outputting a warning when bad characters are detected. VTAdmin simply will not work if someone passes an invalid Cluster ID (current behavior). This PR adds that warning.

Related Issue(s)

First part of #15721

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

• Apply the release notes (needs details) label if users need to know about this change.
• New features should be documented.
• There should be some code comments as to why things are implemented the way they are.
• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• Is this flag really necessary?
• Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
• If the workflow needs to be marked as required, the maintainer team must be notified.

Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.25%. Comparing base (f118ba2) to head (4c10a9d).
Report is 280 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16034      +/-   ##
==========================================
- Coverage   68.40%   68.25%   -0.16%     
==========================================
  Files        1556     1541      -15     
  Lines      195121   197170    +2049     
==========================================
+ Hits       133479   134569    +1090     
- Misses      61642    62601     +959     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[github-actions]

This PR is being marked as stale because it has been open for 30 days with no activity. To rectify, you may do any of the following:

• Push additional commits to the associated branch.
• Remove the stale label.
• Add a comment indicating why it is not stale.

If no action is taken within 7 days, this PR will be closed.

[github-actions]

This PR was closed because it has been stale for 7 days with no activity.