draft: generate certificate and serve over http and https

[JakeChampion]

pushing this up to see if there is interest in seeing this feature land and if this approach is along the right tracks

TODO:

• [ ] Allow certificate to be provided via cli flag
• [ ] Allow certificate to be provided via fastly.toml
• [ ] Allow http and https port to be defiend via cli flag

[arayaryoma]

I have a high expectation of this! We really need it to run our Compute services with secure context to debug cookie behavior(related: https://github.com/fastly/Viceroy/issues/50) and satisfy requirements of our internal backends.

[kpfleming]

This seems really promising! In addition to the TODOs above, have you considered allowing the user to provide a list of SAN(s) to be included in the cert, so that they can test with their 'real' name for the service?