Make the custom CA work with Mastodon.py

[jernst]

This is overall improving things with the Mastodon Node, although more work remains.

• Make the random domain a bit longer
• Better name for our custom CA
• Add x509 SubjectAlternativeName to cert: apparently python ssl needs it
• Added types-requests dependency to make mypy happy
• Mastodon.py can now create the OAuth app using our custom CA

[jernst]

It's only used by Nodes that auto-provision an instance and need a local hostname and cert (ie UBOS Nodes right now). Doesn't affect any other nodes.