Synced from eclipse/che issue

https://github.com/eclipse/che/issues/21724

Is your enhancement related to a problem? Please describe

GitHub Enterprise Server customers have the option to enable/disable subdomain isolation. URLs to GitHub resources depend on this configuration:

<table>
<tr>
<td>Path without subdomain isolation
<td>Path with subdomain isolation
<tr>
<td>`http(s)://HOSTNAME/raw/`
<td>`http(s)://raw.HOSTNAME/`
</table>

Describe the solution you'd like

A Dev Spaces admin should be able to specify if subdomain-isolated is enabled or not in CheCluster CR:

spec: 
  gitServices: 
    github: 
      - endpoint: 'https://github.com'
        secretName: github-oauth-config
        disableSubdomainIsolation: true 

And Che server should use paths with or without subdomain isolation, when resolving GitHub files, based on that configuration.

Note: GitHub suggest to enable subdomain-isolation so when not specified we assume that disableSubdomainIsolation: false (that's also the github.com config anyway)

Release Notes Text

In GitHub Enterprise Server subdomains can be isolated (as it's the case for github.com) and it's now supported by Eclipse Che.