release-24.3: raft: ensure leaderMaxSupported does not regress when bumping terms

[blathers-crl]

Backport 1/1 commits from #133873 on behalf of @arulajmani.

/cc @cockroachdb/release

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Previously, it was possible for a leader to regress leaderMaxSupported by calling an election at a higher term. This was because we weren't careful to recognize this case on the leader, and followers had special case handling that allowed a leader to override inFortifyLease. Together, this could cause lease regressions for LeaderLeases in some rare cases.

This patch fixes this issue by removing special case handling in inFortifyLease. We also remove a special case in the handling of MsgHup which allowed a leader to step down and campaign without de-fortifying itself.

Fixes #133764

Release note: None

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Release justification: Fixes a GA blocker.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

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[cockroach-teamcity]

This change is