Improve documentation on debugging the controller locally

[pjbgf]

The DEVELOPMENT.md could be improved to help users trying to debug problems or reproduce reported issues.

Things we could expand on:

• Suspend objects that are irrelevant to the test at hand.
• Environment variables
  • HOSTNAME: set to source-controller.
  • RUNTIME_NAMESPACE: limit the namespaces being watched.
• Arguments
  • --concurrent: decreasing concurrency to 1.
• Configuring cross-controller interactions.

[alliasgher]

Opened #2034 for this.