Document migration path from Task with PipelineResource to Workspace

Linked to SRVKP-825 and SRVKP-824 we need to document the migration path required from tasks/pipelines using PipelineResources to Workspaces (and results).

• New doc on How to migrate you tasks and pipelines
• Update the release note to make sure we warn users and link to this doc
• Document (if not done) that the devconsole pipeline builder only works with Task with PipelineResources