Dockerfile improvements

[chytreg]

• use alpine because it’s slimmer than buster
• use entrypoint https://phoenixnap.com/kb/docker-cmd-vs-entrypoint
• extend path to easily invoke sendria binary -add no-quit param as default changed after CR
• allow to build any version using build-arg
• fix maintainer deprecation https://docs.docker.com/engine/reference/builder/#maintainer-deprecated

[msztolcman]

Hi @chytreg, Thank you for your contribution. I was playing with Dockerfile for sendria some time ago in dockerfile-playgames branch, but I think it's too complicated and don't want to merge it. Your version is very good: simple and readable, works fine for most usages, doesn't contain stuff specific for development (as @Arzaroth requested some time ago). And I think I should follow this way, for dev-specific we can (and will do) create separate Dockerfile.

The only thing I don't want to is --no-quit argument as default. It's easy to add it when you are starting sendria, but there is no easy way to drop it - you must override whole entrypoint to do this. Could you please remove just this one thing? Then I will merge your PR. Thanks!

[msztolcman]

@chytreg Thanks! Merged :)