Allow User Profile fields to be set and updated via SAML/SCIM

When GitLab accounts are provisioned through SAML or SCIM, the initial user profile contains only essential information: Name/username/email address. Instance administrators or the Users themselves are then required to manually apply any additional details: their Job Title, Organisation, location, etc

In larger environments, the administrative overhead from this is less than ideal.
Furthermore, that a company is unable to 'lock down' or update/correct their employee's account details, such as Job Title, poses a potential social engineering risk (where the user profile could be used to verify a false claim).

Proposal

Make it possible for SAML and SCIM attributes from an Identity Provider to populate and update GitLab user profile fields.