Add Documentation Section on how to migrate to kapp-controller

Users that are considering switching to kapp-controller from another solution need to invest a significant amount of effort to answer the following questions:

1. Is the migration possible for my usecase?
2. How do I perform the migration?
3. How do the concepts in the tool that I am currently using and familiar with map to concepts in kapp-controller?
4. Is kapp-controller at feature parity with the tool that I am currently using?

To answer questions around migration requires the users to become an expert at kapp-controller and the tool they are migrating from. Creating a documentation section called "Migrate to kapp-controller" that provides an easy to follow narrative that guides the user along what they need to learn & do to migrate can be very valuable and accelerate the adoption of kapp-controller.

No files, tests, or documentation entry points are named. Start by locating the existing kapp-controller documentation and identifying the migration source tools to cover. The section is done when it explains feasibility, migration steps, concept mappings, and feature parity for users switching from another solution.

Written by the indexing model from the issue text.