Include post ID in custom metadata

[sanmai]

Description

Let's add a post ID to the custom metadata.

https://docs.parse.ly/api-custom-metadata/

CC @medeiros-amanda @rebeccahum @robersongomes

Motivation and context

Injecting post IDs will let Parsely link back to the edit form of the post.

As compared to LD-JSON (#2510), we can expect that there are no SEO implications.

How has this been tested?

LD-JSON works as usual.

Screenshots (if appropriate)

Summary by CodeRabbit

• New Features

  • Added custom metadata related to post ID for enhanced metadata handling.

• Bug Fixes

  • Improved metadata accuracy by including post ID in metadata.

• Tests

  • Updated tests to cover new metadata additions and ensure proper rendering in JSON-LD scripts and meta tags.