Create more structured documentation for dynamic imagebuilding

[jnywong]

Tasks

• Ensure we hit our definition of well-documented
  • Discoverable on docs.2i2c.org
  • Value and outcomes
  • Expected behavior
  • Who can access it / how to enable it
  • Team documentation to support it
• Read the VEDA docs on this and decide whether to incorporate any of them, see Add docs for build your own image feature NASA-IMPACT/veda-docs#186
• Improve the repo2docker documentation so that we can link users to it: Do one round of documentation improvements to repo2ocker docs infrastructure#5500
• Ask for feedback from community members about this (maybe max jones and chuck and alex mandel from VEDA?)

References

• Quickstart docs added here: [docs, 4h timebox] Write quickstart guide for dynamic image building infrastructure#6357
• Initial implementation: Create a plan for user facing documentation about the 'build your own image' feature infrastructure#5343
• VEDA docs implementation: Add docs for build your own image feature NASA-IMPACT/veda-docs#186

Context

We need documentation to accompany the 'build your own image' feature. This isn't yet rolled out to all hubs, but so we should make that clear, but document the value and "how to" of this feature.

[choldgraf]

I have a little PR here to document this:

• Clean up the image building guide and rearrange environment docs a bit #262