throttler: formal gRPC calls in endtoend tests, removing HTTP API calls

[shlomi-noach]

Description

For v22

This PR removes any references to /throttler/* API calls, and uses gRPC instead.

This is to be done in v22 (right after v21 is released) because some endtoend tests and functionality is used in upgrade/downgrade testing and needs to keep supporting HTTP endpoints.

Related Issue(s)

#15624

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 67.52%. Comparing base (2c10c95) to head (5eeb5f6).
Report is 13 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #16530   +/-   ##
=======================================
  Coverage   67.52%   67.52%           
=======================================
  Files        1594     1595    +1     
  Lines      259564   259605   +41     
=======================================
+ Hits       175266   175304   +38     
- Misses      84298    84301    +3     

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

🚀 New features to boost your workflow:

• ❄ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[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.

[shlomi-noach]

Online DDL flow - Upgrade Downgrade Testing will only pass once release-21.0 is done.

[shlomi-noach]

Just a typo fix here.

[shlomi-noach]

This is now ready to review.

[shlomi-noach]

Actually I see some more throttler API usage around the codebase, so taking this PR back to Draft and pushing more changes.

[shlomi-noach]

Good to review!

[deepthi]

❤️