Add url and metadata for two product entities #15567

[mayixiaobai248]

Related to issue #15567 for adding metadata to channel listings.
This commit introduces two new fields, url and metadata, to the ProductChannelListing and ProductVariantChannelListing entities. These changes address the following needs:

The url field provides a link to the sales channel listing, allowing users to navigate straight to the product on different marketplaces.
The metadata field is a JSON field that enables the storage of additional information.

Impact

• New migrations
• New/Updated API fields or mutations
• Deprecated API fields or mutations
• Removed API types, fields, or mutations

Docs

• Link to documentation:

Pull Request Checklist

• Privileged queries and mutations are either absent or guarded by proper permission checks
• Database queries are optimized and the number of queries is constant
• Database migrations are either absent or optimized for zero downtime
• The changes are covered by test cases
• All new fields/inputs/mutations have proper labels added (ADDED_IN_X, PREVIEW_FEATURE, etc.)
• All migrations have proper dependencies
• All indexes are added concurrently in migrations
• All RunSql and RunPython migrations have revert option defined

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[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}