[v24.3.x] tests/gtest_raft_rpunit: monitor_test_fixture to honour leadership changes

[vbotbuildovich]

Backport #23398 to branch v24.3.x. This issue was created as a placeholder because the original PR's commit(s) could not be automatically cherry-picked.
Here are the commands to execute:

git checkout v24.3.x
git checkout -b manual-backport-23398-v24.3.x-373
git cherry-pick -x d1ecf0e4de 796e6d62f9

git push origin manual-backport-23398-v24.3.x-373
gh pr create \
  --title "[v24.3.x] tests/gtest_raft_rpunit: monitor_test_fixture to honour leadership changes" \
  --base "v24.3.x" \
  --label "kind/backport" \
  --head "manual-backport-23398-v24.3.x-373" \
  --draft \
  --repo "redpanda-data/redpanda" \
  --milestone "v24.3.x-next" \
  --body "Backport of PR https://github.com/redpanda-data/redpanda/pull/23398 "

JIRA Link: [CORE-8887](https://redpandadata.atlassian.net/browse/CORE-8887)

[bashtanov]

#24923