[v24.2.x] pandaproxy/sr: Fix normalized rendering for custom options

[vbotbuildovich]

Backport #24856 to branch v24.2.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 v24.2.x
git checkout -b manual-backport-24856-v24.2.x-921
git cherry-pick -x 44da70e866 cca81edac0 b2785967bb 057ec1293d a46feb43cf f15e7e4216 0ec5585a31 f8c11ae7b7

git push origin manual-backport-24856-v24.2.x-921
gh pr create \
  --title "[v24.2.x] pandaproxy/sr: Fix normalized rendering for custom options" \
  --base "v24.2.x" \
  --label "kind/backport" \
  --head "manual-backport-24856-v24.2.x-921" \
  --draft \
  --repo "redpanda-data/redpanda" \
  --milestone "v24.2.x-next" \
  --body "Backport of PR https://github.com/redpanda-data/redpanda/pull/24856 "

JIRA Link: [CORE-8862](https://redpandadata.atlassian.net/browse/CORE-8862)