Migrate to github.com/rbretecher/go-postman-collection

[grokify]

Migrate to dedicated Postman Collection package:

github.com/rbretecher/go-postman-collection by Romain Bretécher

This is similar to how spectrum/openapi3 is built on github.com/getkin/kin-openapi.

This is pending support for Description objects. This may not be needed if Postman defaults to text/markdown for string type, similar to OpenAPI Spec 3 description, however investigation is needed.

rbretecher/go-postman-collection#14

[grokify]

Added to https://github.com/rbretecher/go-postman-collection/releases/tag/v0.5.0