Update Appendix C COSE examples - based on interop code

[EskoDijk]

• This adds a set of scripts + Makefile to build the certs + examples (PVR, RVR, Voucher) that use COSE signing
• The script code in the Appendix also needs to be changed to reflect this - will do in a separate PR.
• Based on ot-Registrar implementation in https://github.com/EskoDijk/ot-registrar/
• Original organization of old examples (stok.nl) was kept
• Different company "Custom-ER, Inc." was added to be clearly different than the IoT device maker.
• More explanation of what we see in the various data structures.
• Scripted line breaks applied to get below <= 72 char limit. No manual polishing!

[EskoDijk]

Closes #244 #245 #246 #247

[EskoDijk]

Closes #215 (still to be verified by some other codebase that signatures work)

[EskoDijk]

@mcr Thanks! I just added a commit with .ext file changes needed for running it with OpenSSL 3.x (as opposed to 1.x). Examples are regenerated.