feat: Add stars.add and stars.remove methods

[dax]

No description provided.

[abdolence]

Hey, I'm fine with the changes in general, but I wonder if you aware of this update from Slack:

Stars can still be added via stars.add but they can no longer be viewed or interacted with by end-users. Additionally, the star_added event is no longer emitted. We recommend retiring any app functionality that relies on stars APIs.

[dax]

Yes, I know about the deprecation of stars.
Actually stars.list does not work anymore (ie. it always send a empty list) but we can still receive events for "save for later" (add or remove) items as star_added and star_removed events.

Same, the methods stars.add and stars.remove still work for "save for later" items. Unfortunately, there is no "save for later" public API yet so I will rely on the stars API as long as it works 🤷

[abdolence]

LGTM 👍🏻