[Podscribe] New hashed_email properties field

[pitronalldak]

Hi Segment Team,

Scope of this pull request:

• Add a new parameter, user_id, to the settings for the Podscribe destination.

• Add a new field, hashed_email, to the destination. Some of our customers do not want to send raw emails to Podscribe. I am unsure about the correctness of the implementation. Is there a clearer way for customers on the Segment platform to send only hashed emails to the Podscribe destination?

Testing

• [x] Added unit tests for new functionality
• [x] Tested end-to-end using the local server
• [x] [If destination is already live] Tested for backward compatibility of destination. Note: New required fields are a breaking change.
• [ ] [Segmenters] Tested in the staging environment
• [ ] [Segmenters] [If applicable for this change] Tested for regression with Hadron.