Consider supporting additional SAML assertion formats

What

Support a wider range of SAML assertion names for email/firstname/lastname/name.

E.g. Given name, family name, and URL style names.

These can be things like http://schemas.xmlsoap.org/ws/2005/05/identity/claims/emailaddress, E-mail Address, email, and email_address. Similarly name has a variety of forms we should research an accept.

These should apply to both self hosted 'Instance SAML' and GitLab.com's 'Group SAML'

Why

Sometimes identity providers are configured by default with different values to the ones we accept.

Additionally, Group owners who configure GitLab are sometimes different people to the admins configuring the identity provider. If we support a wider range of potential names for assertions we can save GitLab owners from having to reach out to other teams during configuration.