TabletServer: execute DDLs without timeout

[shlomi-noach]

Description

See description in #16710

The implementation is:

• Once we get a query Plan
• And find that the type is PlanDDL
• We replace the existing context (which is a context.WithTimeout()) with a context.WithoutTimeout() (new in go1.21).

Seeking advice on how to test this.

Related Issue(s)

Fixes #16710

Checklist

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[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 68.92%. Comparing base (1ed18d0) to head (1004173).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vttablet/tabletserver/tabletserver.go	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16711      +/-   ##
==========================================
- Coverage   68.93%   68.92%   -0.01%     
==========================================
  Files        1565     1565              
  Lines      201682   201684       +2     
==========================================
- Hits       139020   139002      -18     
- Misses      62662    62682      +20     

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[deepthi]

The way to run long-running DDLs is through ApplySchema. query-timeout at tablet level is supposed to apply to everything. @harshit-gangal will come back with an alternate proposal to solving this feature request.

[shlomi-noach]

Closing in favor of #16735