Parametrize container names

[oyale]

There's a corner case in which we would want to run two separate promtail's containers: when pushing logs to more than one Loki instance:

It is generally recommended to run multiple Promtail clients in parallel
if you want to send to multiple remote Loki instances.

Source

To accomplish that, we need to be able to change the default container name in the docker-compose.yml.j2 template.