allow innodb_lock_wait_timeout as system variable

[harshit-gangal]

Description

This PR adds the support for innodb_lock_wait_timeout to be a user-adjustable system variable.
This PR also fixes the issue with the global scope variable, by preventing to return the session-modified system variable.

Related Issue(s)

• Resolves Feature Request: Allow innodb_lock_wait_timeout variable to be set by DB client #16582

Checklist

• 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]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.76%. Comparing base (eb29999) to head (d3b6db6).
Report is 79 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16574      +/-   ##
==========================================
+ Coverage   68.69%   68.76%   +0.06%     
==========================================
  Files        1547     1556       +9     
  Lines      198297   199812    +1515     
==========================================
+ Hits       136228   137396    +1168     
- Misses      62069    62416     +347     

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