Add/Upgrade weekStart preference for Teams and Organizations

[Cleymax]

• Add validation, default for Organization weekStart preference
• Add weekStart preference for Team

Valid days are the same as those in the web UI.

Reference:

• https://grafana.com/docs/grafana/latest/developers/http_api/preferences/#get-current-user-prefs

[github-actions]

In order to lower resource usage and have a faster runtime, PRs will not run Cloud tests automatically.
To do so, a Grafana Labs employee must trigger the cloud acceptance tests workflow manually.

[julienduchesne]

Before this can be merged, the tests will have to be fixed:

=== CONT  TestAccResourceOrganizationPreferences_WithDashboardID
    resource_organization_preferences_test.go:20: Step 1/5 error: Error running pre-apply refresh: exit status 1
        
        Error: expected week_start to be one of ["sunday" "monday" "saturday" ""], got Monday
        
          with grafana_organization_preferences.test,
          on terraform_plugin_test.tf line 18, in resource "grafana_organization_preferences" "test":
          18:   week_start = "Monday"

[julienduchesne]

Looks good! Thanks