[release-1.15] fix(ovn-central): recover from invalid raft headers

[zhangzujian]

What type of this PR

• Bug fixes
• Tests

What this PR does

This backports #7112 to release-1.15 from squash commit bdec52c1e85d1cee4b9a891c5d74fafe7f36a8c0.

• Rejects zero, missing, or mismatched RAFT header cluster IDs and zero server IDs.
• Discovers and validates the live cluster ID for up to 60 seconds before recovery fallback.
• Preserves the original server ID when rebuilding a member, avoiding a stale fourth RAFT member.
• Archives failed recovery artifacts and only uses clean bootstrap when no valid recovery path remains.
• Writes RAFT header snapshots atomically.
• Adds deterministic leader-checker recovery regression tests.
• Adds the existing AtomicWriteFile helper from fix: install CNI config and binaries atomically #7035 because this maintenance branch predates that helper; unrelated CNI changes from fix: install CNI config and binaries atomically #7035 are not included.

The master-only test/e2e/ha package does not exist on this maintenance branch, so the HA E2E part of #7112 is intentionally excluded instead of introducing a new E2E suite during a backport.

Verification

• bash -n dist/images/start-db.sh
• GOMEMLIMIT=2GiB GOMAXPROCS=2 go test ./pkg/ovn_leader_checker ./pkg/util -count=20
• GOMEMLIMIT=2GiB GOMAXPROCS=2 go test -race ./pkg/ovn_leader_checker ./pkg/util -count=1
• GOMEMLIMIT=2GiB GOMAXPROCS=2 go vet ./pkg/ovn_leader_checker ./pkg/util
• targeted modernize analysis for pkg/ovn_leader_checker and pkg/util
• targeted golangci-lint for pkg/ovn_leader_checker and pkg/util
• git diff --check origin/release-1.15...HEAD

Related issue

• Backport of fix(ovn-central): recover from invalid raft headers #7112
• [BUG] Invalid raft header (.hdr, zero cluster ID) permanently crash-loops ovn-central; db-missing resurrection path has no validation/cleanup (not covered by #7039) #7110

[coveralls]

Coverage Report for CI Build 30870638578

Coverage increased (+0.08%) to 25.047%

Details

• Coverage increased (+0.08%) from the base build.
• Patch coverage: 27 uncovered changes across 2 files (45 of 72 lines covered, 62.5%).
• No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
pkg/util/file.go	33	18	54.55%
pkg/ovn_leader_checker/ovn.go	39	27	69.23%

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	55667
Covered Lines:	13943
Line Coverage:	25.05%
Coverage Strength:	0.29 hits per line

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💛 - Coveralls