Make group availability the default tab when visiting availability page

[seancfong]

Summary

When creating a new meeting, the /availability/[slug] route shows the personal availability tab as the default, and the group availability tab as an option.

Let's try to fix this by considering some options:

1. Make the group availability tab the default tab when navigating to the page
2. Remove the tabs altogether, so you add personal availability by clicking on a button

[seancfong]

@kylebtran Let's try option 2 first with a similar user flow as other meeting scheduling apps. Meanwhile, I'll submit a UI/UX ticket and get their opinions on what is best.