Enable "entrypoint.d" for Connect image

[rstub]

Uses the ideas at https://www.camptocamp.com/en/news-events/flexible-docker-entrypoints-scripts as starting point.

By adding new scripts to /docker-entrypoint.d/ one can add additional steps to the start-up process. And if one runs the image with CMD=bash one gets into a state where all these steps have been applied.

[aronatkins]

What behavior do we want if any part errs?

[aronatkins]

Does this still modify the inherited environment?

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}