Deprecate --v2-deprecation and schedule to remove it in 3.8

[ahrtr]

Resolve #18994

cc @fuweid @serathius @ivanvc @jmhbnz

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.76%. Comparing base (7e04bd2) to head (f54c8f5).
Report is 2 commits behind head on main.

Additional details and impacted files

Files with missing lines	Coverage Δ
server/config/v2_deprecation.go	92.30% <ø> (ø)
server/embed/config.go	79.49% <ø> (ø)
server/embed/etcd.go	75.82% <100.00%> (+0.04%)	⬆️
server/etcdmain/config.go	66.66% <100.00%> (-0.23%)	⬇️

... and 21 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19006      +/-   ##
==========================================
- Coverage   68.77%   68.76%   -0.01%     
==========================================
  Files         420      420              
  Lines       35629    35629              
==========================================
- Hits        24503    24501       -2     
- Misses       9696     9700       +4     
+ Partials     1430     1428       -2     

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[ahrtr]

/test pull-etcd-integration-1-cpu-amd64