What and why

Closes #4729.

st2 <resource> delete only accepted a single positional id, so bulk removal (e.g. after installing a testing pack with many action aliases) required one invocation per resource:

st2 action-alias delete pack.alias1 pack.alias2   # failed before this change

Changes

• ResourceDeleteCommand now takes nargs="+" and loops over the provided ids, mirroring how st2 <resource> get already handles multiple ids.
• A success message is printed for every deleted resource (same wording as before).
• Ids which are not found are reported with the usual <Resource> "<id>" is not found. message; the remaining ids are still attempted and the command exits with a non-zero return code afterwards, so partial bulk deletes are visible to scripts.
• Single id behavior is unchanged: a missing resource still fails with the same message and non-zero exit code.
• ActionDeleteCommand and KeyValuePairDeleteCommand were refactored to override the new delete_resource() hook instead of run(), so they automatically support multiple ids too. As a side effect, st2 action delete <missing-id> now exits non-zero like the other delete commands (it previously exited 0).
• Added a CHANGELOG entry.

Testing

• New unit tests in st2client/tests/unit/test_commands.py:
  • multi-id delete happy path (all ids deleted),
  • partial failure (continues past a missing id, one DELETE issued, exits non-zero),
  • all ids missing (reported + exits non-zero),
  • shell-level test covering every delete-capable resource for both multi-id and single-id not-found cases.
• Ran pytest st2client/tests/unit locally (Python 3.11): 241 passed; the only failures are 4 pre-existing environment-related failures which also fail on unmodified master.
• black --check and flake8 (repo config) are clean on the changed files.

Drafted with AI assistance; reviewed and tested locally.