Add postgres password to docker-compose and example config

[adelavega]

• For security purposes
• @rwblair note that you will have to add a POSTGRES_PASSWORD key to .env for local testing.

[codecov-io]

Codecov Report

Merging #552 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #552   +/-   ##
=======================================
  Coverage   84.59%   84.59%           
=======================================
  Files          39       39           
  Lines        1675     1675           
=======================================
  Hits         1417     1417           
  Misses        258      258

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