The `postHandleMessage` function is parsing links and adding them to the
EmbedCache table if necessary. In the previous implementation, message
updates would push to the embeds unconditionally.

This commit parses links from the message and:

1. Normalizes the URLs
  - Useful for deduplicating similar URLs
2. Remove embeds with matching normalized URLs
  - Leaves all embeds except for ones with a `.url` property matching
  the updated message
  - This allows embeds to be re-ordered if the URL is moved
3. If no normalized URLs are found, remove all embeds
4. Take the deduplicated + normalized URLs and add an embed to the message and
insert into the EmbedCache table (if necessary)

This enables:

1. Embeds to be re-ordered by re-ordering links
2. Embeds to be removed by removing links

and fixes:

1. Duplicate embeds being attached to a message when edited