Updated App Engine Sidekiq + Rails tutorial to work with split health checks

[MoHayat]

Hello -- I opened an issue a few days ago regarding the sidekiq tutorial being outdated and thought I'd submit the fixes that I made to get my background worker instance running and passing the health checks.

Specifically, here's what I changed with the tutorial:

1. instructed users to save or copy password used for Redis instance and add it as an environment variable in app.yaml and worker.yaml, since the linked guide states that setting up a password is important to protecting the instance.
2. in Option B of the deployments, added instructions to install and configure the sidekiq_alive gem to make the background worker instance pass the health checks. I also replaced the health_check attribute with liveness_check and readiness_check configurations, since health checks have been phased out
3. added my github username in authors section to be tagged in case any future users had questions regarding my approach (am I allowed to do this?).

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[MoHayat]

@googlebot I signed it!

[ToddKopriva]

Thanks for the fix. We'll review it soon.

[ToddKopriva]

@chingor13 , could you have a look at this suggested fix for a document that you contributed?

[ToddKopriva]

For reference, here is the issue report:
https://github.com/GoogleCloudPlatform/community/issues/1529

[chingor13]

LGTM, but I haven't worked with GAE flexible environment in quite some time.

[ToddKopriva]

Thanks for the review, @chingor13 .

I'll do an editorial review and then merge the fix.

[ToddKopriva]

Thanks for the fix, @MoHayat .

I'll publish these changes within a couple of days.

[MoHayat]

Sounds great, I appreciate all the help!