[UI/BE] Add Gitlab support for Create/Delete Cluster

[AlinaGoaga]

To test Gitlab Auth:

• set up a Gitlab app (add the relevant redirect URI) and grab the client id and secret
• start the clusters service with CAPI_CLUSTERS_NAMESPACE=default CAPI_TEMPLATES_NAMESPACE=default GITLAB_CLIENT_ID=xxx GITLAB_CLIENT_SECRET=yyy GIT_PROVIDER_TYPE=gitlab GIT_PROVIDER_HOSTNAME=gitlab.com CAPI_TEMPLATES_REPOSITORY_URL=https://gitlab.com/alina48/test-alina CAPI_TEMPLATES_REPOSITORY_BASE_BRANCH=main ENTITLEMENT_SECRET_NAMESPACE=wego-system ENTITLEMENT_SECRET_NAME=weave-gitops-enterprise-credentials WEAVE_GITOPS_FLUX_BIN_PATH=$(which flux) go run cmd/clusters-service/main.go

In this PR:

• added an endpoint to return repo URL (/config)
• PR Preview becomes optional (steps nav updated also, gitops is on screen from the start)
• refactoring of profiles (taking them out of the react json schema wrapper)
• implement Gitlab Auth support
• refactoring of GitAuth components and flow to allow data to persist on screen whilst the auth is in process
• library updated to 0.5.1
• removed the PR Preview acceptance tests temporarily (Saeed will rewrite them when back from holiday)

[foot]

Well done! 🎉 !!!

Thanks for all your hard work on this 💪