New OIDC ID and secret for OIDC-Agent in default oCIS installs

oCIS by default has an OIDC client ID and secret set/hardcoded for the Desktop client:
client-id=xdXOt13JKxym1B1QcEncf2XDkLAexMBFwiT9j6EfhhHFJhs2KM9jbjTmf8JBXE69
client-secret=UBntmLjC2yYCeHwsyj73Uwo9TAaecAetRwMw0xYcvNL9yRdLSUi0hUAHfvCHFeFh

This is recommended to be used for the OIDC-Agent when using RClone. https://owncloud.dev/clients/rclone/webdav-sync-oidc/

However, this does not truly reflect the client in use. I would suggest another client-id and secret is added to the defaults to separate OIDC-Agent from the Desktop Apps.

This would provide better distinction to the user, for debugging and for logging.

_Originally posted by @nicholas-wilson-au in https://github.com/owncloud/client/issues/10256#issuecomment-1651860195_