More API Utilities

[TBHGodPro]

Add some more capabilities to the API, such as:

• Providing the messageTs property of sessions in more places
• Provide the goal id in the /api/goals/:slackId API
• Allow changing the goal of an active session by POSTing to the /api/goals/:slackId API
• Allow viewing shop info (spendable tickets, tickets pending review, tickets in orders, tickets spent) by GETting the /api/shop/:slackId API

[techpixel]

I'm wary of integrating these api changes because the API is already unstable & would add more to manage on our end (such as errors and bugs). If you can prove extensively that this works & works efficiently, I'll merge it.

[TBHGodPro]

All of these endpoints are entirely based off code from separate areas of the repo, especially the slack bot, and as usual anything that is done is always checked beforehand to be valid

I'm confident that the only way these endpoints would break are also ways that the normal bot would break, which just provides a quicker way to find already-existing issues while also assisting users of the api