Add ability to run Sidekiq inline for testing

Problem

For some areas of the app, mainly during feature tests we might want to validate the job's execution, to accomplish this we want to enable the sidekiq inline testing mode on demand for some blocks of code but we don't have the configuration in place today to do so.

Proposal

To improve end to end testing we want to allow the jobs to run inline when executing some tests. To do this we want to configure sidekiq for testing in the same way it is configured for Gitlab to be able to use blocks:

Sidekiq::Testing.inline! do
...
end

to wrap the test parts where we don't want the execution to wait for the job to be done.

Reference: https://github.com/mperham/sidekiq/wiki/Testing

Result

Next steps (if any)

How will we measure success?