[APP-705] Metrics revamp pt2 (#896)

* export track function from analytics.tsx

* fix create account tracking

* fix tracking sign in

* add custom feed events

* fix type errors

* refactor create post event

* add profile follow & unfollow events

* refactor PostsFeedSliceModel into its own file

* refactor PostThreadItemModel into its own file

* reorganize code a lil bit

* refactor post-thread-item to use post-feed-item model under the hood

* add post events

* add post reply tracking

* track custom feed load more

* track list subscribe and unsubscribe

src/view/com/posts/FeedSlice.tsx

@@ -1,6 +1,6 @@
 import React from 'react'
 import {StyleSheet, View} from 'react-native'
-import {PostsFeedSliceModel} from 'state/models/feeds/post'
+import {PostsFeedSliceModel} from 'state/models/feeds/posts-slice'
 import {AtUri} from '@atproto/api'
 import {Link} from '../util/Link'
 import {Text} from '../util/text/Text'