Address missing Sidekiq 7 middleware inclusions

[gpacuilla-st]

Is your feature request related to a problem? Please describe.

It appears that this is not working with sidekiq 7+ currently.

There's some notes around changes in Sidekiq 7 related to this I think:

https://github.com/sidekiq/sidekiq/blob/5b3e895/docs/middleware.md

Middleware Changes in Sidekiq 7.0
tl;dr - middleware should now include Sidekiq::ClientMiddleware or Sidekiq::ServerMiddleware.

Currently, that's not implemented here: https://github.com/elastic/apm-agent-ruby/blob/636319c/lib/elastic_apm/spies/sidekiq.rb

Describe the solution you'd like

Implement the necessary Middleware changes for Sidekiq 7

Additional context

Currently, we aren't seeing any instrumentation being reported for background jobs submitted from our application (sidekiq client side) nor from the bundle exec sidekiq (server side) process which is running separately. Sidekiq is using redis which also never shows up as a dependency in the Kibana Observability APM view.

Relevant gem versions:
rails 7.0.7
sidekiq 7.1.3
redis 5.0.6
elastic-apm 4.7.0

For reference others have also had issues with this, before sidekiq 7: #73

I believe we should at least be seeing the transactions from the server side (bundle exec sidekiq process) going by this:
https://github.com/elastic/apm-agent-ruby/blob/636319c/lib/elastic_apm/spies/sidekiq.rb#L60-L66

[gpacuilla-st]

This is embarrassing, this actually seemed to be working but was hidden in the UI:

I still wonder if the middleware inclusion should be addressed however.