Improve che-plugin.yaml (and devfile) format

[l0rd]

Description

This is issue is to address some comments that have been identified in PR redhat-developer/devfile#2:

• Use of the property mountProjectSources (or even the simpler mountSources) for a tool/plugin [Improve che-plugin.yaml] Use of the property mountProjectSources (or even the simpler mountSources) for a tool/plugin #12413
• Add the ability to specify subPath of a volume [Improve che-plugin.yaml] Add the ability to specify subPath of a volume #12414
• Improve che-plugin.yaml fields names [Improve che-plugin.yaml] Rename some fileds #12415
  • public should become an endpoint attribute
  • consider renaming Devfile#dockerimageTool#endpoints[]#targetPort field to port [WIP] Made several changes in Devfile format redhat-developer/devfile#2 (comment)
  • consider renaming Devfile#dockerimageTool#services field to endpoints to sync che-plugin.yaml and Dockerimage tool models https://github.com/redhat-developer/devfile/pull/2/files#diff-238112cd9401c996e39c118cb7008fdcR19

[sleshchenko]

Also:

• consider renaming Devfile#dockerimageTool#endpoints[]#targetPort field to port [WIP] Made several changes in Devfile format redhat-developer/devfile#2 (comment)
• consider renaming Devfile#dockerimageTool#services field to endpoints to sync che-plugin.yaml and Dockerimage tool models https://github.com/redhat-developer/devfile/pull/2/files#diff-238112cd9401c996e39c118cb7008fdcR19

[metlos]

Note I've split #12413 into more fine grained issues:

• Implement mountSources boolean attribute in che-plugin.yaml Implement mountSources boolean attribute in che-plugin.yaml #12510
• Support mountSources for non-plugin tools in devfile Support mountSources for non-plugin tools in devfile #12554
• Support custom environment variables for tools in devfile Support custom environment variables for components in devfile #12555
• Implement a way for the devfile author to specify the root path of the projects. Implement a way for the devfile author to specify the root path of the projects. #12531
• Support checkoutPath in devfile Support clonePath in devfile #12557
• Support autodetection of checkoutPath of projects Support autodetection of clonePath of projects #12558
• Support reassigning of env variables in che-plugin.yaml Support reassigning of env variables in che-plugin.yaml #12577