[Documentation] Breaking change in 0.39.0: switch from secrets to credentials

[davidcornu]

While upgrading our instance from 0.38.0 to 0.39.0 we had to switch from using Rails secrets to credentials because of this change (https://github.com/Shopify/shipit-engine/pull/1326/files#diff-b2e066ed79ba733982401273e1c6373dbd28c3e3b9ebf62482b5c31c7bbdf3fcR294) where Shipit switched from using Rails.application.secrets to Rails.application.credentials.

I would recommend documenting this in the release notes for 0.39.0 so others making the same upgrade know about it ahead of time.

[casperisfine]

Yeah, Rails.application.secrets were unfortunately deprecated, so we had to migrate over. Changelog is a good call.

[casperisfine]

Hum, actually it is already in the release notes:

* Migrate from legacy Rails secrets to credentials (#1326)
  * Rails secrets were [deprecated in Rails 7.1](https://github.com/rails/rails/pull/48472)
  * [Guide on credentials](https://guides.rubyonrails.org/security.html#custom-credentials)

[davidcornu]

@casperisfine Ohhh it's in the changelog but not in the GH releases notes: https://github.com/Shopify/shipit-engine/releases/tag/v0.39.0

[casperisfine]

Arf, didn't know about GH releases. I'll see if I can edit it.

[simi]

🤔 seems it wasn't reflected at https://github.com/Shopify/shipit-engine/blob/main/docs/setup.md#updating-the-configsecretsyml