[v23.2.x] cluster: publish total available reclaim size to balancer

[vbotbuildovich]

Backport #16354 to branch v23.2.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 v23.2.x
git checkout -b vbotbuildovich/backport-16354-v23.2.x-929
git cherry-pick -x 930db9f0c9e3828656895a80c4d8c0fecaeed029 20e10636780195e0ca1dc8b6d79a3ad998466c05

git push origin vbotbuildovich/backport-16354-v23.2.x-929
gh pr create \
  --title "[v23.2.x] cluster: publish total available reclaim size to balancer" \
  --base "v23.2.x" \
  --label "kind/backport" \
  --head "vbotbuildovich/backport-16354-v23.2.x-929" \
  --draft \
  --repo "redpanda-data/redpanda" \
  --milestone "v23.2.x-next" \
  --body "Backport of PR https://github.com/redpanda-data/redpanda/pull/16354 "