Improve SAML SSO wording

What does this MR do and why?

Update the wording on the login screen when visiting a group with SAML SSO enforce on.

Closes #369567 (closed)

Screenshots or screen recordings

Before

After

How to set up and validate locally

It is kind of tricky to test locally the whole SAML workflow. Maybe the easier way it's, once login, go to this page: https://gdk.test:3443/groups/flightjs/-/saml/sso

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