Allow to define VS Code extensions preferences in Che plugin registry

[gattytto]

this feature will allow 2 things:

1. set default static configurations for extensions that don't implement the use of ENV_VARS from within plugin's meta.yaml and avoid having to set them in the devfile scope.

2. fix things that need to be set in a specific way when extension A needs to change the behavior of extension B, example:
   set java engine from lombok extension's meta.yaml without the 2 extensions having to be mashed up in the same plugin (producing a duplicate of references to vsix that need to be updated separately).

as a consequence this feature will prevent:

1. extensions from downloading content from internet that can be previously populated in the sidecar

2. having to "edit" extensions code to adapt them for sidecars.

example cases of this problem:
kotlin
lombok

[ericwill]

I think this one is a good candidate for a bump in priority -- we are seeing this use needed for multiple extensions:

• kotlin
• haskell
• plantuml

[gattytto]

this may be related

[gattytto]

I think this one is a good candidate for a bump in priority -- we are seeing this use needed for multiple extensions:

• kotlin
• haskell
• plantuml

maybe add lombok to the list :P

[tsmaeder]

And the "official" vale plugin: https://github.com/errata-ai/vale-vscode