[release-19.0] Bump to v19.0.1-SNAPSHOT after the v19.0.0 release

[systay]

Includes the changes required to go back into dev mode (v19.0.1-SNAPSHOT) after the release of v19.0.0.

[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

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If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
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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 67.43%. Comparing base (97fdf78) to head (91bb97e).

Additional details and impacted files

@@              Coverage Diff              @@
##           release-19.0   #15418   +/-   ##
=============================================
  Coverage         67.42%   67.43%           
=============================================
  Files              1560     1560           
  Lines            192642   192642           
=============================================
+ Hits             129896   129914   +18     
+ Misses            62746    62728   -18     

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