(docker, local) PUB_VERTD_URL in environment, localhost default

[flhorizon]

Hello, following up #182:

Would it be possible (and reasonable) to move PUB_VERTD_URL from a build ARG to an ENV variable ?

Or at least making it possible to override at runtime by

environment:
  - OVERRIDE_PUB_VERTD_URL

and adding localhost:24153 as a fallback to either the build arg (if keeping it) or the environment variable (if replacing the arg).

Thank you!

[azurejelly]

#142