Remove hostnamePatterns from credential files (#1030)

Motivation:
We decided to repurpose the `MirrorCredential` to manage all repository credentials, not just those specific to mirroring. The hostnamePatterns property, which was specific to mirroring, is no longer necessary. With the introduction of a dedicated mirroring API, hostnamePatterns can be safely removed.

Modifications:
- Added a job that removes the `hostnamePatterns` property from existing credential files. This prepares the system for the complete removal of this property in the next PR.
- Remove `MirroringMigrationService` to avoid conflict while executing the job.

Result:
- The `hostnamePatterns` property is now deprecated and will be removed entirely in the subsequent PR.