Add transaction_timeout session variable

[mhamza15]

Description

Add a transaction_timeout session variable. The timeout used will be the smaller value of the session variable or --queryserver-config-transaction-timeout.

Related Issue(s)

#18554

Checklist

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

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[mhamza15]

I chose to add this only to ExecuteOptions, although I saw that many fields were both in the overall Session and ExecuteOptions. Query timeout, for example, was in both, but not sure if there's an overall pattern I should be following.

[harshit-gangal]

This is right place for transaction_timeout.
For query timeout, it can be overriden by query comments so it cannot be part of execute options. As we want to send only authoritative value down after applying the override rules.

[codecov]

Codecov Report

❌ Patch coverage is 85.18519% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 67.52%. Comparing base (8d90d26) to head (d2dd377).
⚠️ Report is 64 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtgate/engine/set.go	66.66%	2 Missing ⚠️
go/vt/vtgate/executor.go	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18560      +/-   ##
==========================================
+ Coverage   67.49%   67.52%   +0.03%     
==========================================
  Files        1607     1613       +6     
  Lines      263104   263803     +699     
==========================================
+ Hits       177569   178133     +564     
- Misses      85535    85670     +135     

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[harshit-gangal]

add some e2e test for it.

[harshit-gangal]

This also require website doc update

[mhamza15]

Will do!

[harshit-gangal]

Doc: https://vitess.io/docs/22.0/concepts/query-rewriting/

[mhamza15]

vitessio/website#2001