Add Developer Menu option for switching between Production and Staging

[bjtitus]

Description

Currently we use a different build configuration for staging and production. This makes it difficult for non-developers to test the staging configuration.

Step-by-step reproduction instructions

1. Open Developer Menu
2. Toggle "Staging" on

Screenshots or screen recording

No response

Did you search for existing bug reports?

• [X] I have searched for existing bug reports.

Device, Operating system, and Pocket Casts app version

No response