feat: add field to webpush options to allow for Declarative Web Push messages

[acrobid]

See issue here:

#2892

Spec proposal:

See https://pr-preview.s3.amazonaws.com/w3c/push-api/pull/385.html#declarative-push-message

API Changes

This change allows for a new optional property in the webpush options, and will not affect existing projects.

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[lahirumaramba]

Hey @acrobid, thank you for your contribution we appreciate it! I don't think this feature is currently supported by the BE REST service so adding it to the SDK wouldn't address the issue.

Hey @chong-shao could you add more context here, please? Thank you!

[chong-shao]

Yes, please refer to #2892 (comment) for context

[acrobid]

My understand is that declarative web push has now landed in the specifications.

mdn/browser-compat-data#28000