[v24.2.x] rptest: make target_min_capacity_wanted more deterministic

[vbotbuildovich]

Backport #23484 to branch v24.2.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 v24.2.x
git checkout -b vbotbuildovich/backport-23484-v24.2.x-407
git cherry-pick -x d9a8239ac9

git push origin vbotbuildovich/backport-23484-v24.2.x-407
gh pr create \
  --title "[v24.2.x] rptest: make target_min_capacity_wanted more deterministic" \
  --base "v24.2.x" \
  --label "kind/backport" \
  --head "vbotbuildovich/backport-23484-v24.2.x-407" \
  --draft \
  --repo "redpanda-data/redpanda" \
  --milestone "v24.2.x-next" \
  --body "Backport of PR https://github.com/redpanda-data/redpanda/pull/23484 "

[andrewhsu]

closing this issue because bug was fixed in backport with merge of PR #23602

reissued backport command and new PR was successfully created: #23606