[Nix] Attempt to start mariadb on every nix develop

Summary:
Avoid developers from having to start mariadb-up manually.

This takes the nix run .#mariadb-up workflow, and just makes
it implicit on each nix develop

Eventually the redis service will also need to be supported, so I
designed the service creation to handle multiple services starting
at the same time.

https://linear.app/comm/issue/ENG-1622

Test Plan:

# If you have mariadb setup through homebrew, then run:
brew services stop mariadb

nix develop

Should see:

$ nix develop
View MariaDB Logs: tail -f $HOME/.local/share/MariaDB/logs
Kill MariaDB server: pkill mariadbd
Welcome to Comm dev environment! :)
[12:12:57] jon@Jons-MacBook-Pro ~/comm/comm (master)

Reviewers: abosh, varun, O1 Nix, ashoat

Reviewed By: abosh, O1 Nix, ashoat

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D4875