Ask a user to remove installer from a workspace when they enables WS.NEXT editor or plugin

[garagatyi]

Description

Now we can enable WS.NEXT editor and plugins from UD. And we even have UI for that on the creation of a workspace. But this UI allows a user to enable WS.NEXT plugins without disabling Che 6 installers.
This PR would prevent the start of such a workspace and that would mean that UD would create invalid WS from UI.
It would be a way better UX if we adapt UD to these changes and show user pop-up dialog to remove installers from the workspace if the user tries to enable plugin/editor. We can also add a link to docs about that (they are missing for the time being as far as I know).

Reproduction Steps

OS and version:

Diagnostics:

[garagatyi]

@ashumilova FYI

[garagatyi]

Fix from Angel was merged and now a workspace with plugins enabled on workspace creation view can't be created because server side doesn't allow to create a workspace with installers and plugins at the same time. Seems that we need to implement this issue to avoid this weird UX.
@ashumilova WDYT?

[ashumilova]

we took to the current sprint