[#183] Resolve "script backup generation on remote machine"

Closes #183 (closed)

Reproducing MR message from that card's description because i am TIIIIIIRED AF:

Behavior

• This card implements (most of) the server side scripting necessary for automated backups
• It provides a bin/db/backup script that:
  • produces encrypted backups of a psql dump and the docker volumes of the db and signal keystore
  • encrypts those backups to @margot and @aguestuser
• It does not:
  • scp those backups onto a target machine
  • provide any scripting for restoring from backups
  • do anything via ansible
  • create any new ssh keys for the host machine to use to access the backup target
• All of the undone things are left for #40 (closed)
• This increases the likelihood that we will backup manually more frequently by making it more easier, and tries to help #40 (closed) get done sooner

Side Effects

• It also provides a lot of random scripts that it would have been nice to have on the server while investigating the outage that made us realize backups were a super duper urgent issue!