Feature/docs

[bkneis]

This PR updates the OSS docs to include two new sections, "tutorials" and "concepts" to provide the left two sections of https://diataxis.fr/

The aim is to provide more information on how devpod works, so users understand it's value and helping when determining compliance. The tutorials section's aim is to provide guides on how users can perform common tasks / workflows and to advertise new features (such as remote cache).

There are some PUML diagrams in docs/uml used to generate the diagrams in the docs. @Piotr1215 I would appreciate your feedback here if there is anything I can improve with the UML / annotations. I used C4 notation as I really liked it and found a low barrier to entry if your already familiar with PUML.

@pascalbreuninger @janekbaraniewski please can you review the diagrams themselves fully and ensure I have not misunderstood or got something technically wrong.

Lastly I have added some docblocks and performed some re factoring as I was looking around the code to check if the docs were correct. Some of this was making certain statements more idiomatic but mostly it was renaming. I found a lot of the code had long fully qualified names and duplicate words once the package identifier was included, i.e. devcontainer.FindDevContainer. I know naming is very subjective so I only changed what I thought was awkward to read.