Add the possibility to create SSO users

[fastlorenzo]

Problem statement
It would be great when adding users to the platform that are meant to authenticate via SSO that they do not receive a welcome email asking them to setup their password.

Expected behavior

1. Go to 'Users'
2. Click on '+'
3. Check the box "SSO User"
4. User is created with is_sso flag to true
5. User receive a welcome email that only has the link to the platform and doesn't contain an initial request to setup the password.

Mock
See above

Additional context
When using SSO (SAML) in the platform