add reference docs for device type and job examples

[tang-mm]

Add doc for Supported Provisioning methods and example definition
(moved from https://github.com/canonical/certification-lab-docs/tree/main/reference)

[mz2]

I think only this file actually really belongs in the testflinger docs as a reference, the others are a straightforward fit to Library.

This indeed should also be a reference so that there's an example configuration included (and a hello-world type payload at the top of the file indicating where the choice of the provisioning method goes?)

[mz2]

I think this should effectively be split in two: you have a short reference section there needed into this repo, but most of this should move into Library. When you make this move, please also make an associated removal at the other end (or link in those docs where the current location of the up to date copy is).

[tang-mm]

Updated per comments:

• kept only the provisioning reference doc
• added examples for provision_data fiedl

[tang-mm]

Closed as some contents were covered by #113