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
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• 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

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[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     

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