Allow adding user to cirun resource access

[aktech]

See conda-forge/conda-smithy#2194 (and conda-forge/.cirun#25 (comment))

After the above is implemented, we need to call the conda-smithy cli with something like --cirun-users to be able to allow adding user to cirun resources, so that pull requests like these: conda-forge/.cirun#25 can be automatically created by @cirun-bot when admin requests calls conda-smithy with this param, which in turn passes it to cirun client.

cc @jaimergp