Synced from Eclipse Che issue

https://github.com/eclipse/che/issues/21577

Is your enhancement related to a problem? Please describe

We want to make it simpler for admin to configure Git services in Che (GitHub, Gitlab, BitBucket): it should not be necessary to look at Eclipse Che documentation.

This first issue is about the CheCluster CR update. There will be another issue dedicated to some new chectl parameters to configure git services.

Describe the solution you'd like

spec:
   components
   containerRegistry
+  gitServices:
+    github:
+      - secretName: github-oauth-config
+    gitlab:
+      - secretName: gitlab-oauth-config
+        endpoint: https://gitlab.com
+    bitbucket:
+      - secretName: bitbucket-oauth-config
+        endpoint: https://bitbucket.org
   devEnvironments
   networking

The oAuth App id/secret/private.key etc... should not be directly in the CR (no clear text passwords in the CR). The secret field of an oauthApp is the name of an existing Kubernetes Secret that includes the base64 encoded id and secret. That should be documented clearly in the CRD field to avoid that admins need to read Eclipse Che documentation.

Release Notes Text

Configuring Git services OAuth will be more straightforward for administrators as it's possible to reference Git servies secrets from CheCluster CRs. On OpenShift those new configuration will be available from the OpenShift Console UI.