[Key Vault] Update administration changelog for 4.0.0b3
# Release History
-## 4.0.0b3 (Unreleased)
+## 4.0.0b3 (2021-02-09)
+### Added
+- `KeyVaultAccessControlClient` supports managing custom role definitions
+
### Breaking Changes
- Renamed `KeyVaultBackupClient.begin_full_backup()` to `.begin_backup()`
- Renamed `KeyVaultBackupClient.begin_full_restore()` to `.begin_restore()`
- `not_actions` -> `denied_actions`
- `not_data_actions` -> `denied_data_actions`
- Renamed `KeyVaultRoleAssignment.assignment_id` to `.role_assignment_id`
+- Renamed `KeyVaultRoleScope` enum values:
+ - `global_value` -> `GLOBAL`
+ - `keys_value` -> `KEYS`
## 4.0.0b2 (2020-10-06)
### Added
