Update RRM snippet placement logic

[nfmohit]

Feature Description

The Reader Revenue Manager snippet placement logic should be updated to enable conditional and context-aware snippet placement, as follows:

• If the current screen is a singular post, the following logic will be used in said order:
  • The googlesitekit_rrm_{Publication ID}:productID post meta setting will be checked.
    • If its value is none, no snippet will be added to the post.
    • If its value is anything other than an empty string, the snippet will be added with the value of the post meta setting as the product ID.
  • Otherwise, all taxonomy terms attached to the post will be queried and each attached term will be checked for a googlesitekit_rrm_{Publication ID}:productID term meta setting (if possible, a meta query will be used to query all terms with the meta set). The value for the first found match will be checked.
    • If its value is none, no snippet will be added to the post.
    • If its value is anything other than an empty string, the snippet will be added with the value of the term meta setting as the product ID.
  • Otherwise, the snippetMode module setting will be checked.
    • If it is per_post, no snippet will be added.
    • If it is post_type, it will be checked if the post type of the current post belongs to the postTypes array module setting.
      • If not, no snippet will be added.
      • If yes, the snippet will be added with the value of the productID module setting as the product ID.
    • If it is sitewide, the snippet will be added with the value of the productID module setting as the product ID.
• If the current screen is not a singular post, the following logic will be used:
  • The snippetMode module setting will be checked.
    • If it is sitewide, the snippet will be added with the value of the productID module setting as the product ID.

If none of the above conditions are met, no snippet will be added.

• See relevant section in the design doc.

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Implementation Brief

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Changelog entry

[nfmohit]

@aaemnnosttv While brainstorming the ACs for this issue, I realised that I did not consider an edge-case scenario. Suppose, in a certain post, the RRM tag is not added based on the above logic. However, the user has added the inline button block (#9963). Since we're not adding the snippet, the button will not work. Do you have a suggestion on how we can address this edge-case? Thank you!