[v24.1.x] [CORE-8797] Improve parsing of POST /subject/{subject}/version object

[vbotbuildovich]

Backport #24860 to branch v24.1.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 v24.1.x
git checkout -b manual-backport-24860-v24.1.x-6
git cherry-pick -x c68eeef9eb 821a0402be

git push origin manual-backport-24860-v24.1.x-6
gh pr create \
  --title "[v24.1.x] [CORE-8797] Improve parsing of POST /subject/{subject}/version object" \
  --base "v24.1.x" \
  --label "kind/backport" \
  --head "manual-backport-24860-v24.1.x-6" \
  --draft \
  --repo "redpanda-data/redpanda" \
  --milestone "v24.1.x-next" \
  --body "Backport of PR https://github.com/redpanda-data/redpanda/pull/24860 "

[CORE-8797]: https://redpandadata.atlassian.net/browse/CORE-8797?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

JIRA Link: [CORE-8901](https://redpandadata.atlassian.net/browse/CORE-8901)