Publish API documentation for PackageCollectionsModel

[heckj]

Description

Used by package collection tooling, the PackageCollectionsModel should have API reference documentation published akin to what's available for PackageDescription

Expected behavior

No response

Actual behavior

No response

Steps to reproduce

No response

Swift Package Manager version/commit hash

No response

Swift & OS version (output of swift --version && uname -a)

No response