This must be done outside of a Makefile environment due to how it
affects the programs that run inside `make`. `sops exec-env` will
decrypt a file and export the values as environment variables for the
program specified, which in this case is the user's shell.
This commit also includes a `.sops.yaml` file with the three PGP keys
from the Makefile and regenerates the DigitalOcean PAT.