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

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[codecov]

Codecov Report

Attention: Patch coverage is 54.54545% with 25 lines in your changes missing coverage. Please review.

Project coverage is 67.67%. Comparing base (9383943) to head (7e83225).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtgate/vtgate.go	24.00%	19 Missing ⚠️
go/vt/vtgate/static_config.go	33.33%	4 Missing ⚠️
go/vt/vtgate/viper_config.go	83.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17419      +/-   ##
==========================================
- Coverage   67.67%   67.67%   -0.01%     
==========================================
  Files        1583     1584       +1     
  Lines      254363   254384      +21     
==========================================
+ Hits       172140   172143       +3     
- Misses      82223    82241      +18     

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[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?

[GuptaManan100]

For now, its only being used for the txmode property, and that too mostly in tests (just 1 instancd of vtexplain_vtgate using it other than tests). I think it should be okay to specify them explicitly from the tests.