tweak docker containsers to avoid ERROR: connected to template database, exiting

[akuzm]

On a clean docker container timescale/timescaledb:latest-pg12', we get an error in server log:

ERROR:  TimescaleDB background worker connected to template database, exiting

This error happens if the background workers are attached to a database with datistemplate. This can happen if you install the extension into a database that you want to use as a template and then start the background workers. It has no consequences, but is alarming for the users and we should investigate whether something can be tweaked in the docker startup scripts to avoid the error.