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

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