[Sentry] Track time to content on home feed

[mplorentz]

Create a Sentry transaction to track how long our app takes from startup until the user sees content. Let's name this HomeFeed.initialLoad.

This transaction should be started when the home feed is displayed to the user and finish when new notes are displayed. Let's tag the transaction with the number of notes displayed and number of seconds between the current date and the first note in the list. Ideally we would have spans that measure the amount of time spent 1) fetching content from Core Data and 2) rendering notes. If the spans are too complex to implement lets discuss alternatives.

Let's be careful only to track this transaction when the user actually navigates to the home feed. If we show onboarding or the Discover tab first then only start the transaction when the user navigates to the home feed.

Additionally, create a widget in our Sentry dashboard or three that we can use to see how long these transactions take on average. The goal here is to understand how long our users wait to see content and how recent the content they see is.