Rename`[repository]` `DISABLE_MIRRORS` to `[mirror]` `DISABLE_NEW_PULL` and add `ENABLED` and `DISABLE_NEW_PUSH` with the below meanings:
- `ENABLED`: **true**: Enables the mirror functionality. Set to **false** to disable all mirrors.
- `DISABLE_NEW_PULL`: **false**: Disable the creation of **new** mirrors. Pre-existing mirrors remain valid.
- `DISABLE_NEW_PUSH`: **false**: Disable the creation of **new** push mirrors. Pre-existing mirrors remain valid.
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: delvh <dev.lh@web.de>
