Figure out what to do with html.manifest.serviceworker.*

[captainbrosset]

According to MDN, the following BCD keys are for Just-In-Time (JIT)-installation and registration of a web-based payment app providing a payment mechanism for a specified payment method in a merchant website. This is part of the PaymentHandler API:

• https://developer.mozilla.org/en-US/docs/Web/Manifest/serviceworker
• https://developer.mozilla.org/en-US/docs/Web/API/Payment_Handler_API

BCD keys:

• html.manifest.serviceworker
• html.manifest.serviceworker.scope
• html.manifest.serviceworker.src
• html.manifest.serviceworker.use_cache

For now, I've kept them as ignored BCD keys in manifest.yml because I lack the subject matter expertise to move them somewhere else.

@ddbeck mentioned that they could move to payment-handler.yml instead, and that seems like the right thing to do, but I'd prefer if something more versed in the Payment Handler API commented on this first.

Originally posted by @captainbrosset in #2078 (comment)