Support mountSources for non-plugin tools in devfile

[metlos]

The che plugins can now specify whether or not they want to have the root of source directories mounted
to their containers using the mountSources attribute (which causes the volume with sources to be mounted into the container on location specified by the CHE_PROJECTS_ROOT env variable available to the container).

We should also add this functionality to devfile to support the same mechanism for tools that are not implemented using a che plugin.

• dockerimage tool: This should be easy for dockerImage type (all it has to understand is the CHE_PROJECTS_ROOT variable).
• Kubernetes/OpenShift tool: Not sure how to exactly apply it to kubernetes list though. Reference devfile example: https://github.com/redhat-developer/devfile/blob/master/Devfile.yaml

[sleshchenko]

It is already implemented for dockerimage tool in the following PR #12649

[sleshchenko]

The issue with mountSources for k8s/os components is the following:
Currently mountSources is a boolean and may be specified for dockerimage component only.
For k8s/os component, true/false mountSources would mean that it is/isn't needed to mount sources to all containers of component (there can be multiple pods, with multiple containers inside).
And a user may need more flexibility and it would be nice to provide an ability to specify containers where projects sources are needed. For example, this Devfile[1] contains k8s component that has two containers - mongo and nodejs-app, and only nodejs-app needs projects sources.
The solution here might be introducing a format that is similar to entrypoints:

  - type: kubernetes
    alias: employee-manager
    reference: deploy_k8s.yaml
    sourcesMounts:
    - parentName: podName
      parentSelector:
        labelKey: labelValue
      containerName: nodejs-app

The issue with such format - it is not clear how to specify sourceMounts for all containers of a component.

The possible resolutions of this issue that I see:

1. Implement mountSources: true/false for k8s/os component and mount projects PVC into all containers of k8s/os component. It's easy to implement and use solution but it may slow down some workspaces since undeeded volumes may be used.
2. Investigate more about a possible format that would give an ability to mount projects sources to all containers or specified ones (I assume with parentName, parentSelector, containerName fields).

@skabashnyuk @metlos @mshaposhnik @l0rd WDYT?

[1] https://github.com/sleshchenko/NodeJS-Sample-App/blob/master/devfile.yaml

[l0rd]

@sleshchenko I would not change that now. Your issue makes sense but the solution you propose is still complicated. And I don't consider it urgent because multi-pod workspaces are still not supported currently and for multi-container components we can just continue mounting sources on all containers (or splitted the multi-container component in multiple components with a single container).

[l0rd]

@sleshchenko @skabashnyuk @metlos I figure out that my comment above may be misleading. What I wanted to say is:

• It's important that we support mounting sources for any component type
• In multi-container components we should mount sources on every container
• We can ignore multi-pod workspaces scenarios for now