Allow plugin broker to return plugins that are not explicitly in the devfile

[amisevsk]

Is your enhancement related to a problem? Please describe.

Currently, if the plugin broker returns a ChePlugin whose ID is not referenced in the devfile, the Che server will throw an error and fail workspace startup. However, certain cases require adding/removing plugin definitions during plugin meta.yaml process, e.g. merging plugins (#15373) or processing plugin dependencies (#15376).

Describe the solution you'd like

We should add fields to the internal struct used to pass data back to the Che server to help identify mystery plugins, e.g.

mergedPlugin: true
mergedFrom: [redhat/java11/latest, redhat/quarkus-java11/latest]
# and/or
isDependency: true

and then process this on the backend to ensure additional metadata is attached correctly.

I've added the area/che-theia label since a component of this would be making sure the merged/dependent plugin is surfaced correctly in the Theia UI.

Additional context

Related issues:

• [meta.yaml / Che plug-ins]: Add dependencies section [meta.yaml / Che plug-ins]: Add dependencies section #15376
• Run vsx in same container if the container specs match Run vsx in same container if the container specs match #15373

[che-bot]

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Moderators: Add lifecycle/frozen label to avoid stale mode.

[amisevsk]

Not a problem with devfile 2.0