feat: add saml sso support as the default

[ericwyles]

Description

This PR adds saml protocol support for SSO and sets it as the default. To go back to OIDC, set the value sso.protocol to openid_connect (example in bundle/uds-config.yaml)

Also, when saml is set as the protocol, this also enables granting admin access to gitlab using keycloak group membership. By default, being a member of either /GitLab Admin or /UDS Core/Admin in keycloak will grant GitLab admin access.

Related Issue

Relates to #102

Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [x] Other (security config, docs update, etc)

Checklist before merging

• [x] Test, docs, adr added or updated as needed
• [x] Contributor Guide Steps followed