activity: feed endpoints

[arthyn]

This adds two endpoints specifically for the activity tab with pagination.

/activity/feed/init/{count}.json gives latest items limited by count for each tab

/activity/feed/{type}/{count}/{start}?.json

• count: @ud representing number of items you wish to receive
• start: @ud or @da optional parameter, will only get events before this time
• type: all | mentions | replies
  • all: any post, reply, dm, or dm reply that I was notified for
  • mentions: any message that mentions me
  • threads: any replies for which I was notified for

Also updates the add update to include source and the stringified form of source.

Fixes TLON-2036

PR Checklist

• Includes changes to desk files
• Describes how you tested the PR locally (test ship vs livenet)
• If a new feature, includes automated tests
• Comments added anywhere logic may be confusing without context

[linear]

TLON-2036 activity: pagination on back-end

[Fang-]

As discussed out of band. Mostly just style nits. But looks like it does the right thing.

[arthyn]

@Fang- since you're afk packing and I just implemented what you commented on going to take that as soft approval