[input-plane] Return FunctionRetryPolicy in FunctionHandleMetadata

[rculbertson]

Part of SVC-574

Currently we return the retry policy in FunctionMap. With the new input-plane, this would mean we need to return the retry policy in AttemptStart. But we can simplify things if we instead return the policy in FunctionCreate/FunctionGet. That way this information can come from the control plane, and the input plane doesn't have to know about it at all. See this section of the input-plane API doc for more info.

---

Compatibility checklist

Check these boxes or delete any item (or this section) if not relevant for this PR.

• Client+Server: this change is compatible with old servers
• Client forward compatibility: this change ensures client can accept data intended for later versions of itself

Note on protobuf: protobuf message changes in one place may have impact to
multiple entities (client, server, worker, database). See points above.

---

Release checklist

If you intend for this commit to trigger a full release to PyPI, please ensure that the following steps have been taken:

• Version file (modal_version/__init__.py) has been updated with the next logical version
• Changelog has been cleaned up and given an appropriate subhead

---

Changelog