Replication bug fixes (backport #516)

[mergify]

1. Fix bug where occasionally one follower would receive
   more entries then expected resulting in triggering 2.

2. Fix bug when follower received an append_entries_rpc with
   no new entries in it would trigger an incorrect resend
   scenario when throughput is high.

3. Fix bug where a late written event could accidentally confirm
   unwritten entries in a higher term.

4. A replication liveness bug that could cause clusters to get stuck
   after a member removal.

   ---

   This is an automatic backport of pull request Replication bug fixes #516 done by Mergify.

[mergify]

Cherry-pick of 324d9bc has failed:

On branch mergify/bp/v2.15.x/pr-516
Your branch is up to date with 'origin/v2.15.x'.

You are currently cherry-picking commit 324d9bc.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   src/ra_server.erl
	both modified:   test/ra_log_memory.erl
	both modified:   test/ra_server_SUITE.erl

no changes added to commit (use "git add" and/or "git commit -a")

Cherry-pick of 60c2d19 has failed:

On branch mergify/bp/v2.15.x/pr-516
Your branch is ahead of 'origin/v2.15.x' by 1 commit.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit 60c2d19.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   src/ra_server_proc.erl
	modified:   test/coordination_SUITE.erl
	modified:   test/ra_2_SUITE.erl
	modified:   test/ra_server_SUITE.erl

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   src/ra_server.erl

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally