Add ability to delete, edit or re-try migration plans

Problem Definition

Right now the migration assistant add-ons don't present the ability to delete or re-try migration plans.

This is not a major issue but would be a good enhancement so customers can better track which projects/spaces have been migrated so far and help them re-try failed migrations after applying a possible fix for the last issue that blocked the migration.

Suggested Solution

Enhance the add-ons so users can delete migration plans and re-try plans that failed previously.