feat: Simplify friendships

[dcramer]

This changes the friend model to be mutual acceptance by default vs one-way follows.

It creates a bit of a departure from the model of db => api => ui schemas, where follows in this case no longer map directly to a restful object.

Fixes GH-60

[codecov]

Codecov Report

Patch coverage: 98.39% and project coverage change: -0.32% ⚠️

Comparison is base (98f5b51) 83.87% compared to head (67af80f) 83.55%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #61      +/-   ##
==========================================
- Coverage   83.87%   83.55%   -0.32%     
==========================================
  Files         127      125       -2     
  Lines        9989     9811     -178     
  Branches      847      825      -22     
==========================================
- Hits         8378     8198     -180     
- Misses       1611     1613       +2     

Files Changed	Coverage Δ
apps/api/src/db/schema/enums.ts	100.00% <ø> (ø)
apps/api/src/routes/listFriends.ts	95.45% <92.85%> (ø)
apps/api/src/routes/addFriend.ts	97.26% <97.26%> (ø)
apps/api/src/app.ts	92.07% <100.00%> (+7.92%)	⬆️
apps/api/src/db/schema/notifications.ts	100.00% <100.00%> (ø)
apps/api/src/lib/notifications.ts	69.11% <100.00%> (-19.12%)	⬇️
apps/api/src/lib/serializers/friend.ts	100.00% <100.00%> (ø)
apps/api/src/lib/serializers/notification.ts	93.88% <100.00%> (+1.08%)	⬆️
apps/api/src/lib/serializers/user.ts	98.52% <100.00%> (+0.02%)	⬆️
apps/api/src/routes/addTastingComment.ts	89.06% <100.00%> (ø)
... and 5 more

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