Move to v1alpha3 DevWorkspaces

[amisevsk]

Description

The DevWorkspace API has become cluttered as new features are added. Since a lot of these devfile features duplicate functionality, it would be helpful to create a new API version that is simplified.

• Move to using .spec.project and .spec.dependentProjects instead of .spec.projects, the difference being that .spec.project is a single project (normally implicit in the devfile) and dependentProjects are additional projects to import alongside the single main one (see Dependent Projects api#1082)
  • For conversion, the first project in .spec.projects should probably be treated as .spec.project with the rest as .spec.dependentProjects.
• Remove plugin-type components and move to exclusively using .spec.contributions
  • Conversion is easy, as the objects are the same; labels/annotations may be required to ensure plugins stay plugins after round-trip conversion.
  • This change would likely break Web Terminal, we would need to verify its compatible and work around if not (in particular, terminal customization depends on plugin components). This could potentially be worked around by continuing to use v1alpha2 as the storage version.

Additional context

Most of the preparation work would need to be done in the devfile/api repository.

[amisevsk]

This is not something we can do in the immediate future, but it is something to consider down the line.