refactor: Move conversation functionality into its own task

[dariusc93]

What this PR does 📖

• Move some of the conversation logic into its own task
• Remove individual pinning of messages and perform a recursive pin on the conversation
• Move conversation list into its own document instead of individual documents
• Map the conversation keystore into the root document

Which issue(s) this PR fixes 🔨

• N/A

Special notes for reviewers 🗒️

• This is a breaking change due to each conversation being pushed into its own document rather than individual documents. There is no migration path at this time to move those conversations into the single document

Additional comments 🎤

• This may be changed to push the pointer into the root document of the identity to keep everything together, however performance may vary long term.
• The whole keystore is linked to root document, but most may be invalidated in the future depending on if the conversations exist or persist.