Switch to use semisync source / replica plugins

[dbussink]

The plugins with the old terminology are deprecated and will be removed in the future. In MySQL 8.4.0 also the old terminology for regular replication is removed.

This starts the move to use the new style. Since MySQL 8.0.26 the new semisync plugin is available, so we should start using it from that version on.

This means we also need new default MySQL cnf files to set up things correctly. We add here a mysql8026.cnf and also a pre-emptive mysql84.cnf. The latter is needed to start the work in the future for MySQL 8.4.0. The main change here is that the deprecated mysql_native_password plugin needs to be explicitly enabled.

Removing our usage of mysql_native_password is another separate significant effort. The main issue there is how we want to deal with certificates etc. which end up being required for replication if you want to use caching_sha2_password which adds a whole layer of complexity we've never had to deal with.

Related Issue(s)

Part of #11716

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• Documentation was added or is not required

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[codecov]

Codecov Report

Attention: Patch coverage is 50.65789% with 75 lines in your changes are missing coverage. Please review.

Project coverage is 68.44%. Comparing base (ee6b837) to head (500a31f).

Files	Patch %	Lines
go/vt/mysqlctl/replication.go	68.00%	24 Missing ⚠️
go/vt/vttablet/tabletmanager/rpc_replication.go	18.51%	22 Missing ⚠️
go/vt/mysqlctl/mysqld.go	0.00%	6 Missing ⚠️
go/cmd/vtcombo/cli/main.go	0.00%	5 Missing ⚠️
go/mysql/flavor_mysql.go	37.50%	5 Missing ⚠️
go/vt/mysqlctl/fakemysqldaemon.go	50.00%	4 Missing ⚠️
go/vt/vttablet/tabletmanager/rpc_actions.go	57.14%	3 Missing ⚠️
go/mysql/flavor_mariadb.go	0.00%	2 Missing ⚠️
go/mysql/replication.go	77.77%	2 Missing ⚠️
go/vt/mysqlctl/builtinbackupengine.go	50.00%	1 Missing ⚠️
... and 1 more

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #15791   +/-   ##
=======================================
  Coverage   68.43%   68.44%           
=======================================
  Files        1558     1558           
  Lines      195971   196036   +65     
=======================================
+ Hits       134121   134169   +48     
- Misses      61850    61867   +17     

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[GuptaManan100]

Looks good to me!

[deepthi]

Nice work. I like that you handled some of the tech-debt around not passing a context to some of these functions too.