Switch to using the default caching sha2 password

[dbussink]

After #18033 added forward compatibility in the upcoming v22, we can make it the default in v23.

Related Issue(s)

Part of #17966

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

[vitess-bot]

Review Checklist

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General

• Ensure that the Pull Request has a descriptive title.
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• Apply the release notes (needs details) label if users need to know about this change.
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[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 67.56%. Comparing base (470671c) to head (1df1bf6).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
go/mysql/flavor_mysql.go	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18010      +/-   ##
==========================================
- Coverage   67.58%   67.56%   -0.02%     
==========================================
  Files        1598     1598              
  Lines      260270   260306      +36     
==========================================
- Hits       175902   175886      -16     
- Misses      84368    84420      +52     

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[dbussink]

Alright, in order to be safely able to do this, we first need to ship #18033 with v22 and then we can do this change for v23.