Make transaction mode a dynamic configuration

[GuptaManan100]

Description

This PR makes the changes to allow for transaction mode to be a dynamic configuration.
We already have all the viper changes in place for us to be able to do this. Tests for the same have also been added. I also refactored a little bit of how we create dynamic configs introduced in #17328. The changes allow for us to only instantiate a single dynamic config instance and pass it around everywhere.

While trying to add a /debug/config endpoint to vtgate, I found out that one already exists and it already shows the config values there!

I also found out that we already log changes in configurations too!

I1220 20:57:10.788354   77635 servenv.go:378] Change in configuration - map[config:map[file:/Users/manangupta/vitess/vtdataroot/vtroot_9501/tmp_9503/vtgate-config-9536.json name:vtconfig notfound:map[handling:1] paths:[/Users/manangupta/vitess/go/test/endtoend/transaction/twopc] persistence:map[min_interval:1s] type:] config-file:/Users/manangupta/vitess/vtdataroot/vtroot_9501/tmp_9503/vtgate-config-9536.json config-file-not-found-handling:1 config-name:vtconfig config-path:[/Users/manangupta/vitess/go/test/endtoend/transaction/twopc] config-persistence-min-interval:1s config-type: datadog-agent-host: datadog-agent-port: discovery:map[high_replication_lag:2h0m0s legacy_replication_lag_algorithm:true low_replication_lag:30s min_number_serving_vttablets:2] discovery_high_replication_lag_minimum_serving:2h0m0s discovery_low_replication_lag:30s enable_direct_ddl:true enable_online_ddl:true jaeger-agent-host: legacy_replication_lag_algorithm:true min_number_serving_vttablets:2 trace:map[datadog:map[agent:map[host: port:]] enable-logging:false jaeger:map[agent-host: sampling_rate:0.1 sampling_type:const] service:noop] tracer:noop tracing-enable-logging:false tracing-sampling-rate:0.1 tracing-sampling-type:const transaction_mode:TWOPC vschema_ddl_authorized_users:]

Related Issue(s)

• RFC: Atomic Distributed Transactions #16245

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

Deployment Notes

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

• Apply the release notes (needs details) label if users need to know about this change.
• New features should be documented.
• There should be some code comments as to why things are implemented the way they are.
• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• Is this flag really necessary?
• Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
• If the workflow needs to be marked as required, the maintainer team must be notified.

Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[codecov]

Codecov Report

Attention: Patch coverage is 50.98039% with 25 lines in your changes missing coverage. Please review.

Project coverage is 67.63%. Comparing base (9714713) to head (4d5f6e1).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtgate/vtgate.go	24.00%	19 Missing ⚠️
go/vt/vtgate/staticconfig.go	33.33%	4 Missing ⚠️
go/vt/vtgate/viperconfig.go	75.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17419      +/-   ##
==========================================
- Coverage   67.63%   67.63%   -0.01%     
==========================================
  Files        1581     1584       +3     
  Lines      253860   254060     +200     
==========================================
+ Hits       171708   171825     +117     
- Misses      82152    82235      +83     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[harshit-gangal]

nit: add a comment to explain the purpose of this struct

[dbussink]

@GuptaManan100 It looks like the default for StaticConfig for the DDL settings is different from the default in Vitess, should that always be true by default? We could achieve that by using an initializer function for it instead of a direct struct initialization?

[dbussink]

@GuptaManan100 I think it's still good to have a local reference here? That makes it easier to test also in the future? We could still provide a function like we have today with NewDynamicViperConfig to bind the variables I guess, but it feels a bit more clean to explicitly have it?