Consolidate feature flags

For the dogfood release of FY26Q2 we might want to consolidate feature flags to better control rollout to our GitLab Team Members.

config/feature_flags/wip/allow_organization_creation.yml
config/feature_flags/wip/organization_switching.yml
config/feature_flags/wip/ui_for_organizations.yml

We can merge allow_organization_creation and organization_switching as they don't make sense apart.