Add many more agent config options

[DrJosh9000]

What

Add a subset of agent config options to values.yaml, and more git-related options to checkout params.

Why

There are huge gaps in the configurability of the agent, that so far require:

• building a custom agent image to bake in a custom config, or
• complicated chains of configuration in a pipeline or values file (env var + volume with podSpecPatch + extraVolumeMounts), or
• putting agent config in pipeline-level env vars, that outside this stack are usually prevented from having an effect

There's a need to supply many of the same config options, and also to put a k8s twist on some of them (e.g. instead of hooks-path, what about hooks-volume-source?)

[wolfeidau]

Only one observation / question, great work!