Encrypting `brokers.toml`, account and ledger files for `git`

[goodboy]

Since there's often API keys, special private networking config
stuff and maybe even account numbers stored in this file we should
probably support out of the box git-crypting of some sort to
avoid users being paranoid about their git service providers
😶‍🌫️

Also, obviously users may want to encrypt trades ledgers and
account files from the .accounting subsys so as to not leak their
current positions to the world 😂

Definitely relates to #530 😎

git python APIs

• https://github.com/jelmer/dulwich#getting-started
• TODO add more!

---

git Encryption repos

Here's an off the cuff list of projects that might be handy for
this, mostly pulled from a summary blog
post:

• git-crypt

• https://github.com/AGWA/git-crypt

• https://www.agwa.name/projects/git-crypt/

• git-easy-crypt

  • https://github.com/taojy123/git-easy-crypt
  • https://taojy123.github.io/git-easy-crypt/

• git-remote-gcrypt

  • https://github.com/spwhitton/git-remote-gcrypt
  • https://spwhitton.name/tech/code/git-remote-gcrypt/

• blackbox (from SO oddly enough)

  • https://github.com/StackExchange/blackbox

• docker secrets

  • https://docs.docker.com/engine/swarm/secrets/

prolly more discussion to come.