Missing documentation of flags field in activity

[MinnDevelopment]

The activity object should document the flags field of the activity.

They are bitwise flags that map to already existing data, like if an activity is a spectate activity. Just easier to pipe around numbers than checking for nulls

There are also a few more fields that aren't documented such as session_id and sync_id.

[msciotti]

I think the last thing we landed on is that fields like session_id and sync_id were still in flux, so we don't want to commit to documentation yet. Buuuut I think we said flags are alright? We can probably add those.

[MinnDevelopment]

Would it be possible to add more details to these flags? I find it rather difficult to understand what each flag means even when looking through presences.
What I understood from looking into it:

INSTANCE: start and end timestamps are set
JOIN: join/listen along button (often in combination with SYNC i believe)
SPECTATE: ask to spectate button available*
JOIN_REQUEST: ask to join button available
SYNC: spotify track
PLAY: game can be started from discord?*

* I haven't actually seen these in the wild yet