Allow to specify Che 7 plugin or editor meta.yaml with a link

[garagatyi]

Description

Now we allow adding Che 7 plugin or editor with a custom registry.
Knowing how files are structured in the che plugin registry it is possible to host meta.yaml file in a GitHub repo which is way more convenient than hosting own plugin registry. For example for the development purposes.
We can improve this approach by allowing a direct link to a file without placing it in a specific folder in the repo.
This would make the addition of custom plugins and editors way easier and more convenient.

Reproduction Steps

OS and version:

Diagnostics:

[garagatyi]

Related to #11818

[che-bot]

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