Checklist

[x] Upgrade Jets: Are you using the latest version of Jets? This allows Jets to fix issues fast. There's a jets upgrade command that makes this a simple task. There's also an Upgrading Guide: http://rubyonjets.com/docs/upgrading/
[x] Reproducibility: Are you reporting a bug others will be able to reproduce and not asking a question. If you're unsure or want to ask a question, do so on https://community.rubyonjets.com
[ ] Code sample: Have you put together a code sample to reproduce the issue and make it available? Code samples help speed up fixes dramatically. If it's an easily reproducible issue, then code samples are not needed. If you're unsure, please include a code sample.

My Environment

Software	Version
Operating System
Jets	3.0.4
Ruby	2.5.0

Description

We have an enterprise app running on jets but we have a custom layer for this application, when we try to add our custom layer the deployments fail because it exceeds the layer limit on lambda, I did a quick research and I realized that when I add a custom layer, Jets stills uploading its layer.

Expected Behaviour

if I set this config config.gems.disabled = true on config/application.rb jets should not upload its lambda layer

Current Behavior

when I added my custom layer with this config, the deployment fails because it reaches the layer limit on lambda(size)

# config/application.rb
config.gems.disable = true
config.lambda.layers = ["my_custom_layer_arn"]

Step-by-step reproduction instructions

Code Sample

Solution Suggestion

if a user adds a custom layer, jets should not upload its gem layer, I think we can fix it by adding this condition here

def get_layers(runtime)
  return nil unless runtime =~ /^ruby/
  return Jets.config.lambda.layers if Jets.config.gems.disable

  ["!Ref GemLayer"] + Jets.config.lambda.layers
end

rubyonjets / jets

doesn't include the Jets layer when config.gems.disabled = true #541