cmd/catalyst: implement stack of configuration files

[iameli-streams]

For overriding stuff! This will allow people to better override configuration settings in their development environment and set up the framework for people to run their own boxes in production-like settings.

I'm trying to figure out the new command-line options and it's hard. Braindump:

It's confusing because there's a few operations here:

• 🗒 update-manifest: Update manifest file
• 📩 download: Download new binaries
• 🏗 build-config: Build MistController JSON config from YAML files
• 🔁 roll-mist: Trigger Mist reload for running process (SIGUSR1) (mutually exclusive with exec)
• 🍪 exec: Exec myself to become MistController (mutually exclusive with roll-mist)

Workflow: Boot up a prod server
catalyst

• 🏗 build-config
• 🍪 exec

Workflow: Boot up a canary server w/ a custom manifest pointing at different branches
catalyst --update-manifest --download

• 🗒 update-manifest
• 📩 download
• 🏗 build-config
• 🍪 exec

Workflow: Download binaries from manifest (Dev environment init)
catalyst --download --exec=false

• 📩 download

Workflow: Build a new manifest (CI)
catalyst --update-manifest --exec=false

• 🗒 update-manifest

Workflow: Run an inplace-deploy on a prod server (Manifest from somewhere else)
catalyst --download --roll-mist

• 📩 download
• 🏗 build-config
• 🔁 roll-mist