SidecarDB: Don't ignore table charset and collation

[mattlord]

Description

Any table level character set and collation changes that we wanted to make were previously ignored during tablet init. That caused issues, in particular, with Vitess clusters that have been around for some time or that had modified defaults and e.g. may then be using a mix of utf8mb3 and utf8mb4. This can then lead to a host of unexpected failures when Vitess queries these internal tables, often times joining them with MySQL system tables e.g. in information_schema. In order to ensure consistent expected behavior we should be prescriptive and explicit about the character set and collations we want/expect on the sidecar (internal vitess) tables.

This PR explicitly adds a character set for each sidecar table and modifies the settings used with schemadiff during the sidecar DB init process so that we apply any future changes to these within the code.

Related Issue(s)

• Fixes: Bug Report: SidecarDB init does not apply table level changes #16669

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
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• 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

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.90%. Comparing base (a54d5ec) to head (8fb0607).
Report is 42 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16670      +/-   ##
==========================================
- Coverage   68.93%   68.90%   -0.03%     
==========================================
  Files        1562     1562              
  Lines      200767   200941     +174     
==========================================
+ Hits       138407   138468      +61     
- Misses      62360    62473     +113     

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[shlomi-noach]

LGTM and good catch. We might also just as well "upgrade" to TableCharsetCollateStrict - but as this works then that's fine.