Significantly improve embed for docker updates

[evanugarte]

right now, our embed looks like

lets change it to make it even more readable. to see the json that github sends us, see the associated section in the readme

title of embed

[REPO_NAME:BRANCH] Deployment Successful [FIRST_SEVEN_COMMIT_CHARACTERS](COMMIT_URL_HERE) — COMMIT_NAME

first line

Author: [AUTHOR_NAME_HERE](AUTHOR_URL_HERE), environment: A@B

for A, use the environment variable $USER that you can read in python, for B, use $HOSTNAME, this is also an environment variable

stdout section

only include the stdout if it isnt empty. right now, we include it no matter what, and it takes up space.

we could do the exit codes first, for docker and git, then do the docker and git stdout underneath the exit code section.