Add Shopper Insights Demo feature

[scannillo]

JIRA DTBTSDK-3174

Summary of changes

• This PR takes a "path of least resistance" approach and restores the old PreferredPaymentMethods demo feature (see old file)
• I made only the necessary updates to this file to get it renamed to ShopperInsights & updated for BT iOS V6 API changes
  • Note: This ViewController could use some clean-up, but I figured we can 🏈 punt on it, since we're pretty slammed with feature requests right now (and ShopperInsights will fluctuate a lot the coming weeks)

Checklist

• Added a changelog entry

Authors

@scannillo

[jaxdesmarais]

Not sure if we want to 🏈 on this based on the PR description but subclassing PaymentButtonBaseViewController should allow us to get a lot of this for "free". Specially the createButton and ability to remove the override of the auth init.

[hollabaq86]

I know this is in the Demo app, so not as merchant impacting, but I personally think it's acceptable to take a little time and do this work now. If folks push back we can lean on the company's leadership principles.

[scannillo]

This is a great callout! Addressed in 92676b6

[hollabaq86]

overall looks good, added my two cents on cleanup work now vs later

[hollabaq86]

I know this is in the Demo app, so not as merchant impacting, but I personally think it's acceptable to take a little time and do this work now. If folks push back we can lean on the company's leadership principles.