api: Update `CrossRealmBot` type for server 1.9.0.
api: Update `CrossRealmBot` type for server 1.9.0.

The `avatar_url` field is especially welcome, as it reduces a
discrepancy against `User`.

vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile