Add GetServerStatus RPC to use in PRS

[GuptaManan100]

Description

This PR starts the work for #15946.
In order to use the replica which has the innodb buffer pool loaded the most, we first need the ability to read that said value. This PR adds a new RPC to the tablet manager client interface for this.

In the next release, when this RPC is available on all the vttablets, we can use this RPC instead of PrimaryStatus to check for the availability of all the replicas in PRS. Currently we are throwing away the results of PrimaryStatus. Instead we can call GetServerStatus and even use the results for better choosing the primary candidate.

Related Issue(s)

• Feature Request: Prefer longer running replicas for PRS #15946

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

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[codecov]

Codecov Report

Attention: Patch coverage is 42.25352% with 41 lines in your changes missing coverage. Please review.

Project coverage is 68.21%. Comparing base (0c2856e) to head (347d413).
Report is 15 commits behind head on main.

❗ Current head 347d413 differs from pull request most recent head d2d88bf

Please upload reports for the commit d2d88bf to get more accurate results.

Files	Patch %	Lines
go/vt/mysqlctl/replication.go	0.00%	20 Missing ⚠️
...t/vtctl/grpcvtctldserver/testutil/test_tmclient.go	0.00%	7 Missing ⚠️
go/vt/vtcombo/tablet_map.go	0.00%	5 Missing ⚠️
go/vt/mysqlctl/fakemysqldaemon.go	0.00%	4 Missing ⚠️
go/vt/vttablet/faketmclient/fake_client.go	0.00%	2 Missing ⚠️
go/vt/vttablet/tabletmanager/rpc_actions.go	0.00%	2 Missing ⚠️
go/vt/vttablet/grpctmclient/client.go	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16022      +/-   ##
==========================================
- Coverage   68.24%   68.21%   -0.04%     
==========================================
  Files        1541     1541              
  Lines      197117   197305     +188     
==========================================
+ Hits       134530   134595      +65     
- Misses      62587    62710     +123     

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[mattlord]

Thanks, @GuptaManan100 ! I only had some nits and you can address those are you feel is best.

[mattlord]

IMO it's worth creating a mysqld.FetchQuery helper (doesn't have to be done here) as there should be no need to use the DBA pool for this and various other things.

[GuptaManan100]

We can do that change as a follow up. Currently rushing to get this into RC

[deepthi]

Comments from @mattlord seem worth addressing. Rest LGTM.

[deepthi]

Leaving this to @GuptaManan100 to merge once remaining feedback has been addressed.

[deepthi]

DCO seems to be stuck everywhere. I've manually verified that all commits have the necessary signoff. Bypassing that check to merge.