[KV] Update keys changelog for release
# Release History
-## 4.5.0b4 (Unreleased)
+## 4.5.0b4 (2021-10-07)
### Features Added
- Added `KeyClient.get_cryptography_client`, which provides a simple way to create a
- Added `KeyClient.rotate_key` to rotate a key on-demand
- Added `KeyClient.update_key_rotation_policy` to update a key's automated rotation policy
-### Breaking Changes
-
-### Bugs Fixed
-
### Other Changes
- `CryptographyClient` no longer requires a key version when providing a key ID to its constructor
(though providing a version is still recommended)
