Issue Summary

Add an option that logs a user out of the IdP when they log out of Bamboo. This will a) prevent the user from automatically logging back in with the same account when they access Bamboo again and b) allow the user to log in using a different account without having to end the session with the IdP first.

This is reproducible on Data Center: (yes)

Steps to Reproduce

1. Run Bamboo on version 9.2.4.
2. Configure SAML integration with Bamboo.
3. Successfully log in to Bamboo.
4. Access the Bamboo administration > Overview > Authentication Methods > Edit SAML SSO > Uncheck remember my user logins. 
5. Choose "Logout" and successfully log out.
6. Select login in the top right corner.
7. Choose "Login to your account"

Expected Results

The user is prompted to re-authenticate against the Identity Provider.

Actual Results

The user will not be asked to re-authenticate and will automatically log in to Bamboo if the user's session with the IdP is still valid.

Workaround

Clear the web browser's cache and try logging in again. This should be enough to end the user's session with the IdP and prompt for username/ password.