Define and unify Flux controller standards

[scottrigby]

There are several problems which will be solved by defining and unifying Flux controller standards.

Work on this is well underway. This meta issue is to form specific issues and tasks into a coherent multi-step plan, so that team members can both collaborate and work in parallel to make this effort as efficient and successful as possible.

Linked issues:

• Stage 0: Document runtime package and APIs, provide additional helpers pkg#117
  • README for runtime package pkg#125
• Stage 1: Roll out new unified standards to all Flux controllers #1601
• Stage 2: Flux contributor documentation: Controller fundamentals website#398
• Stage 3: GitOps Toolkit documentation on combining packages to build better controllers website#400

[pjbgf]

The unified standards are defined, but still being improved as they are rolled out across the controllers.
Temporary reference can be found at:

• Controller Patterns
• kstatus conditions
• kstatus - conditions and generations check

[stefanprodan]

I'm closing this umbrella issue for the same reason mentioned here: #1601 (comment)