fix: grafana logout not working in some environments (#559)

## Description
Updated grafana values to include a proper signout url that manages
removing the session from both grafana and keycloak.

Also added the group auth definition to grafana to require that users
have `/UDS Core/Admin` membership ( kind of redundant since it already
requires users be an admin but this will just reinforce that a bit more
).

## Related Issue

Fixes #515 

## Type of change

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

## Checklist before merging

- [x] Test, docs, adr added or updated as needed
- [x] [Contributor
Guide](https://github.com/defenseunicorns/uds-template-capability/blob/main/CONTRIBUTING.md)
followed

src/grafana/values/values.yaml

@@ -32,6 +32,7 @@ grafana.ini:
     name: UDS Identity Service
     auth_url: https://sso.###ZARF_VAR_DOMAIN###/realms/uds/protocol/openid-connect/auth
     token_url: http://keycloak-http.keycloak.svc.cluster.local:8080/realms/uds/protocol/openid-connect/token
+    signout_redirect_url: https://sso.###ZARF_VAR_DOMAIN###/realms/uds/protocol/openid-connect/logout?post_logout_redirect_uri=https%3A%2F%2Fgrafana.admin.###ZARF_VAR_DOMAIN###%2Flogin%2Fgeneric_oauth
     allow_sign_up: true
     # Require a UDS Core group to access Grafana
     role_attribute_path: "contains(groups[], '/UDS Core/Admin') && 'Admin' || contains(groups[], '/UDS Core/Auditor') && 'Viewer' || 'Unauthorized'"