misc(sidekiq): Add sidekiq-pro as an optional dependency

[groyoh]

Context

Today, we are using Sidekiq to handle our background jobs. While it works well for most of our needs, we are reaching some limitations with the open-source version, particularly around job reliability during high load.

Sidekiq uses BRPOP to fetch a job from the queue in Redis. This is very efficient and simple but it has one drawback: the job is now removed from Redis. If Sidekiq crashes while processing that job, it is lost forever.

Description

This adds sidekiq-pro as an optional dependency which can be install when building the Docker image.

This also updated the Dockerfile to:

1. Accept a BUNDLE_WITH which can be used to conditionally enabled Sidekiq Pro when the value is sidekiq-pro.

2. Mount the BUNDLE_GEMS__CONTRIBSYS__COM variable as a Docker secret as it's only required during the build and is a sensitive information.

3. Rely on BUNDLE_WITHOUT env variable instead of the --without command line option to be consistent and because it is deprecated:

   [DEPRECATED] The `--without` flag is deprecated because it relies on being remembered across bundler invocations, which bundler will no longer do in future versions. Instead please use `bundle config set without 'test'`, and stop using this flag
   

Note that we also added a LAGO_SIDEKIQ_PRO_REQUIRED env variable which will cause the app to not boot if Sidekiq Pro is not properly installed.

[julienbourdeau]

Am I correct to understand that oss release will ship without sidekiq pro in the image and you must rebuild the image with your own BUNDLE_GEMS__CONTRIBSYS__COM to use sidekiq pro?

[groyoh]

Am I correct to understand that oss release will ship without sidekiq pro in the image and you must rebuild the image with your own BUNDLE_GEMS__CONTRIBSYS__COM to use sidekiq pro?

Yes.

[IxDay]

One question for you, otherwise it looks good

[groyoh]

Thanks for the review @IxDay 👍