Support CLICKHOUSE_PASSWORD_FILE environment variable in Dockerfile

[Eyal-Shalev]

Use case

I want to pass the db password as a file. Instead of with environment variable.
This is needed if I want to use the docker secrets capabilities of docker-compose without tinkering.

Describe the solution you'd like

In the entrypoint.sh file of the Dockerfile, check if the CLICKHOUSE_PASSWORD_FILE environment variable is set and if it does and points to a file, use it to set the password on the user created in said script (defaults to default)

Additional context

From what I've seen many other database images provide such file. PostgreSQL for example: https://hub.docker.com/_/postgres#:~:text=it%20into%20account.-,Docker%20Secrets,-As%20an%20alternative