Introduce endpoint field/attribute that allows requiring a unique host

[sleshchenko]

Is your feature request related to a problem? Please describe.
The real use-case for it comes from Theia and Webview. As far as I can tell, are both listen to the same port but expect different hosts to be used because of security reasons - everything that is opened through the Webview component should not reach Theia cookies.

The way how Theia declares it in Che currently:
https://github.com/eclipse/che-plugin-registry/blob/master/v3/plugins/eclipse/che-theia/7.22.0/meta.yaml#L33

spec:
  endpoints:
   -  name: "theia"
      public: true
      targetPort: 3100
      attributes:
        protocol: http
        type: ide
        secure: true
        cookiesAuthEnabled: true
        discoverable: false
   -  name: "webviews"
      public: true
      targetPort: 3100
      attributes:
        protocol: http
        type: webview
        secure: true
        cookiesAuthEnabled: true
        discoverable: false
        unique: true

Describe the solution you'd like
We need to agree if a unique host is common enough to introduce a new field for it in Devfile 2.0.
If not - agree on the attribute name that devworkspace controller will use, unique seems to be not self-descriptive. Maybe dedicated-host: true/false

[sleshchenko]

According to the latest discovering, the above is not really true )
devfile 1.0 has requireSubdomain attribute for endpoint, but it's designed to be used by user servers, not Che Theia, and probably with http in case of self-signed certificate is used.
We could run Theia Webview on a dedicated subdomain, but then we would need wildcard or not self-signed certificates.
I'll collect some more details and update this issue a bit later.

[l0rd]

@sleshchenko should we close this issue?

[sleshchenko]

it's going to be a attribute on Che side, and we're not sure it's common enough to put it into model