[v25.2.x] iceberg: blms support

[vbotbuildovich]

Backport #27251 to branch v25.2.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 v25.2.x
git checkout -b manual-backport-27251-v25.2.x-950
git cherry-pick -x 914e25eb7a 2511633e04 067c99c070 f9b8bc62bb

git push origin manual-backport-27251-v25.2.x-950
gh pr create \
  --title "[v25.2.x] iceberg: blms support" \
  --base "v25.2.x" \
  --label "kind/backport" \
  --head "manual-backport-27251-v25.2.x-950" \
  --draft \
  --repo "redpanda-data/redpanda" \
  --milestone "v25.2.x-next" \
  --body "Backport of PR https://github.com/redpanda-data/redpanda/pull/27251 "

JIRA Link: [CORE-13188](https://redpandadata.atlassian.net/browse/CORE-13188)

[CORE-13188]: https://redpandadata.atlassian.net/browse/CORE-13188?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ