Add non-root user by default

[ToshY]

Fixes #679

Based on:

• Run container as an unprivileged user  #679 (comment)
• feat: run docker as non-root le-yak/dunglas-symfony-docker#1

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Using a non-root user is regarded as a best practice.

I am not sure what the "many issues" a non-root user could cause (which might need further explanation), but I was able to build the images (dev/prod targets) and run it on dev without any apparent issues. Requires further testing.

[7-zete-7]

Hi, @ToshY!

Perhaps, instead of changing the Dockerfile, it would make sense to describe the changes to this PR in the documentation page?

[7-zete-7]

I assume FrankenPHP relies on Caddy's decision to run as root by default. See the discussion on this topic in the Caddy repository: caddyserver/caddy-docker#104.

[ToshY]

Hi, @ToshY!

Perhaps, instead of changing the Dockerfile, it would make sense to describe the changes to this PR in the documentation page?

Okay, would you recommend adding a (new) documentation page, or update an existing one?

Edit

I've moved it to a new documentation page.

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I understand the decision to not directly apply the changes to the Dockerfile and document it instead. Maybe something to take into consideration for next time (and start with non-root by default then).

[7-zete-7]

This template's documentation files use simple diffs, not patches.

How about adding a couple of examples of using the new arguments?