[v23.3.x] storage: coroutinize/de-recursify log_reader::do_load_slice

[vbotbuildovich]

Backport #18073 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-18073-v23.3.x-618
git cherry-pick -x 41a7a1a473b92e4006e29d1c319f75538e7feafc

git push origin vbotbuildovich/backport-18073-v23.3.x-618
gh pr create \
  --title "[v23.3.x] storage: coroutinize/de-recursify log_reader::do_load_slice" \
  --base "v23.3.x" \
  --label "kind/backport" \
  --head "vbotbuildovich/backport-18073-v23.3.x-618" \
  --draft \
  --repo "redpanda-data/redpanda" \
  --milestone "v23.3.x-next" \
  --body "Backport of PR https://github.com/redpanda-data/redpanda/pull/18073 "

JIRA Link: [CORE-2670](https://redpandadata.atlassian.net/browse/CORE-2670)

[CORE-2670]: https://redpandadata.atlassian.net/browse/CORE-2670?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

[piyushredpanda]

Merged