Define the devfile 2.0 equivalent of the Devfile 1.0 `chePlugin` `preferences`

[davidfestal]

Is your feature request related to a problem? Please describe.

In Devfile 1.0, there is a way to define preferences for a plugin.

A plugin may need to be precisely tuned and in such case plugin preferences should be used. Example shows how jvm may be configured with plugin’s preferences.

...
- id: redhat/java/0.38.0
  type: chePlugin
  preferences:
     java.jdt.ls.vmargs: '-noverify -Xmx1G -XX:+UseG1GC -XX:+UseStringDeduplication'

cf. also Che documentation: https://www.eclipse.org/che/docs/che-7/end-user-guide/making-a-workspace-portable-using-a-devfile/#_tuning_cheplugin_component_configuration

Describe the solution you'd like

We need to be sure that the Devfile 2.0.0 specification allows to express the equivalent concept, so that the use of Devfile 2.0 in Che will not loose a feature.

We should ensure this before the 2.0.0 Devfile spec release

[elsony]

Is this preference requirement applicable to plugins in general or is this a Che-specific requirement? If it is the former, I think it is fine to introduce the explicit preference field; if it is the later, will it be acceptable to use the generic attribute field to specify the preference?

[elsony]

Closing this based on we'll be using attributes for preferences. There will be a separate discussion to see if plugins are something that we still need to be part of the devfile given that it is specific for Theia usage only.