Update OAuth2 provider scopes in roundcube integration docs

[0t0x]

Issue Starting with authentik 2024.2, this refresh token requires the offline_access scope. Even though it is updated in oauth2 documentation, roundcube docs have not been updated to include specified scope.

Screenshots

[xpufx]

It would be nice to add a note at the bottom alerting people that this changed after a specific version so that they will know immediately what to change in their existing configs.