Fix more v3.6 deprecation comments

[ivanvc]

I did the fixing of the remaining deprecated experimental options:

• ExperimentalTxnModeWriteWithSharedBuffer
• ExperimentalStopGRPCServiceOnDefrag
• ExperimentalInitialCorruptCheck

And also standardized all deprecation messages in server/etcdmain/help.go

Part of #18023

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.94%. Comparing base (7073c41) to head (9c30af2).
Report is 5 commits behind head on main.

Additional details and impacted files

Files with missing lines	Coverage Δ
server/config/config.go	80.23% <ø> (ø)
server/embed/config.go	80.11% <ø> (ø)

... and 20 files with indirect coverage changes

@@           Coverage Diff           @@
##             main   #19408   +/-   ##
=======================================
  Coverage   68.93%   68.94%           
=======================================
  Files         420      420           
  Lines       35757    35757           
=======================================
+ Hits        24649    24652    +3     
- Misses       9683     9684    +1     
+ Partials     1425     1421    -4     

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[ivanvc]

/retest

[ahrtr]

Thank you @ivanvc

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ahrtr, ivanvc

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[ahrtr]

/cherry-pick release-3.6

[k8s-infra-cherrypick-robot]

@ahrtr: new pull request created: #19409

In response to this:

/cherry-pick release-3.6

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