[v23.3.x] storage: Use fragmented_vector in OT-state

[vbotbuildovich]

Backport #16642 to branch v23.3.x. Note that this issue was created as a placeholder, since the original PR's commit(s) could not be automatically cherry-picked.
Here are the commands to execute:

git checkout v23.3.x
git checkout -b vbotbuildovich/backport-16642-v23.3.x-673
git cherry-pick -x ba038617d3f7e94ba1b14894f7c3fa3db598d852

git push origin vbotbuildovich/backport-16642-v23.3.x-673
gh pr create \
  --title "[v23.3.x] storage: Use fragmented_vector in OT-state" \
  --base "v23.3.x" \
  --label "kind/backport" \
  --head "vbotbuildovich/backport-16642-v23.3.x-673" \
  --draft \
  --repo "redpanda-data/redpanda" \
  --milestone "v23.3.x-next" \
  --body "Backport of PR https://github.com/redpanda-data/redpanda/pull/16642 "

[piyushredpanda]

Merged.