Update debian based image, experimental alpine based image, and add example

[k2nr]

See https://degica.docbase.io/posts/104229 for why these base images benefit.

After merging this, I'll add the following tags to the images

• rails-base/debian/2.3 -> 2.3
• rails-base/debian/2.4 -> 2.4
• rails-base/alpine -> alpine

Changes

• Add app user which will eventually becomes a running user of a container
• Add UID build argument to add option to change uid of the running user
  • this is useful for development to make host user ID and container user ID same
• Update ruby version from 2.3.1 to 2.3.3
• Add ruby 2.4 debian base image
• Updated alpine based image (still experimental, prior to beta)
  • Mainly I developed this alpine based image for fun so I'm not planning to use this for our production environment but since alpine is getting popular in docker world and is smaller than debian it's worth researching

[k2nr]

@essa Can you review this?

[k2nr]

@essa ping. Please take a look when you have time

[k2nr]

@essa ping

[essa]

LGTM.

Sorry for late response. I was worrying about compatibility of Rails LTS. It was updated recently and LTS started support for ruby 2.3.

• 101 System requirements - Rails LTS documentation

It was ruby 2.2 when I checked it two weeks ago. So I thought about creating another image for 2.2 myself. But we do not need it now.

I will replace the base image for Basecamp/Extinguisher after the migration.

[k2nr]

@essa Thank you for your review! I don't mean to force you to use this image, however, I believe this base image is far better than the official images so if this base image works easily for your apps I recommend to use but still we can continue to use the official image. no rush but please try this out!