Add Uptime RPC to use in PRS

[GuptaManan100]

Description

This PR starts the work for #15946.
In order to use the replica which has the highest uptime, we first need the ability to select the uptime. 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 Uptime 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 52.83019% with 25 lines in your changes are missing coverage. Please review.

Project coverage is 68.42%. Comparing base (8639de2) to head (bafb0b4).
Report is 5 commits behind head on main.

Files	Patch %	Lines
go/vt/mysqlctl/replication.go	0.00%	7 Missing ⚠️
...t/vtctl/grpcvtctldserver/testutil/test_tmclient.go	0.00%	7 Missing ⚠️
go/vt/vttablet/tabletmanager/rpc_replication.go	0.00%	4 Missing ⚠️
go/vt/mysqlctl/fakemysqldaemon.go	0.00%	2 Missing ⚠️
go/vt/vtcombo/tablet_map.go	0.00%	2 Missing ⚠️
go/vt/vttablet/faketmclient/fake_client.go	0.00%	2 Missing ⚠️
go/vt/vttablet/grpctmclient/client.go	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15947      +/-   ##
==========================================
+ Coverage   68.41%   68.42%   +0.01%     
==========================================
  Files        1562     1562              
  Lines      197056   197105      +49     
==========================================
+ Hits       134807   134864      +57     
+ Misses      62249    62241       -8     

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[GuptaManan100]

Superseded by #16022 since we can directly read the Innodb_buffer_pool_pages_data value instead of relying on the uptime as a proxy for it