Add an advanced option to skip any Gemfile updates

[albus522]

Motivation

Our standard dockerfile-rails update flow is to bump the gem, run rails generate dockerfile, have it overwrite everything, use the git diff to undo anything we don't want. This is getting really close to not requiring undoing anything, with the Gemfile being a notable exception. For us, we know exactly what we do and don't want in our Gemfile, but we don't have the same level of confidence with the docker interactions, which is what we use this gem for. Particularly annoying at the moment is the insistence that Redis is the only way to run ActionCable.

Generally, I would argue that interacting with the Gemfile at all is beyond the scope of what dockerfile-rails should do, possibly with the exception of checking lock platforms, but I suspect that is likely an uphill battle.

Proposed solution

Add an option to skip modifying the Gemfile. I added the option description to the Readme under the advanced section because it's skipping a significant number of touch points.

I went looking for a place to add tests, but it doesn't appear there are currently tests for any of the Gemfile interactions.

[rubys]

Particularly annoying at the moment is the insistence that Redis is the only way to run ActionCable.

That indeed is annoying, and should be fixed. Preferably by scanning Gemfiles and/or config files rather than requiring an option.

Care to take a pass at fixing that? I've invited you to the repository... all I ask is that you maintain the current tests and add new ones when you feel it is appropriate.

[albus522]

I have added an issue to track it (#96), but I don't have the spare time to tackle it immediately. I have an inclination that it should be somewhat straight forward to read the ActionCable config, but I've been doing open source long enough to know there are often hidden dragons.