add missing mapping-groups

[aro-lew]

at the moment you can not do:
user_oidc:provider NAME --mapping-groups xyz

but you can:
occ config:app:get user_oidc provider-1-mappingGroups or [...] config:app:set [...]

this PR adds --mapping-groups to user_oidc:provider

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[julien-nc]

@aro-lew Thanks a lot, this has been fixed in another PR.