Add missing fields to CreateUserOptions struct

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The CreateUserOptions struct is currently missing several attributes that are supported by the GitLab Users API for creating a user.

According to the official documentation:
https://docs.gitlab.com/api/users/#create-a-user

Missing fields:

• Auditor
• ColorSchemeID
• CommitEmail
• Discord
• ExtraSharedRunnersMinutesLimit
• Github
• GroupIDForSAML
• Pronouns
• SharedRunnersMinutesLimit