Extract raft functions into raft directory

[serathius]

This is experiment to move create a raft directory within etcdserver.

[k8s-ci-robot]

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[codecov]

Codecov Report

❌ Patch coverage is 92.35294% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.23%. Comparing base (b868ea1) to head (cc53d7a).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
server/etcdserver/raft/raft.go	92.85%	2 Missing and 5 partials ⚠️
server/etcdserver/server.go	90.32%	2 Missing and 4 partials ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
server/etcdserver/adapters.go	66.66% <100.00%> (ø)
server/etcdserver/bootstrap.go	62.68% <100.00%> (-2.07%)	⬇️
server/etcdserver/metrics.go	77.50% <ø> (-3.36%)	⬇️
server/etcdserver/raft/logger.go	51.35% <ø> (ø)
server/etcdserver/raft/metrics.go	100.00% <100.00%> (ø)
server/etcdserver/v3_server.go	75.48% <100.00%> (-1.06%)	⬇️
server/etcdserver/server.go	82.76% <90.32%> (-0.15%)	⬇️
server/etcdserver/raft/raft.go	88.62% <92.85%> (ø)

... and 51 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #20738      +/-   ##
==========================================
- Coverage   69.14%   66.23%   -2.92%     
==========================================
  Files         420      421       +1     
  Lines       34817    34816       -1     
==========================================
- Hits        24074    23060    -1014     
- Misses       9348    10351    +1003     
- Partials     1395     1405      +10     

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[k8s-ci-robot]

@serathius: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-etcd-verify	cc53d7a	link	true	/test pull-etcd-verify
pull-etcd-grpcproxy-e2e-amd64	cc53d7a	link	true	/test pull-etcd-grpcproxy-e2e-amd64
pull-etcd-grpcproxy-e2e-arm64	cc53d7a	link	true	/test pull-etcd-grpcproxy-e2e-arm64
pull-etcd-e2e-amd64	cc53d7a	link	true	/test pull-etcd-e2e-amd64
pull-etcd-e2e-386	cc53d7a	link	true	/test pull-etcd-e2e-386
pull-etcd-coverage-report	cc53d7a	link	true	/test pull-etcd-coverage-report
pull-etcd-e2e-arm64	cc53d7a	link	true	/test pull-etcd-e2e-arm64

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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