[Fixes #155] Update to Phoenix 1.7.1

[zorn]

Fixes #155

PR code walk: https://www.youtube.com/watch?v=RYOc2nL-qfY

How I approached the upgrade:

• Reading the overall Changelog of Phoenix 1.7
• Reading the upgrade instructions of Chris McCord.
• Using the PhoenixDiff tool to compare the previous version to the newest (1.7.1): https://www.phoenixdiff.org/?source=1.6.15&source_variant=default&target=1.7.1&target_variant=default
• Making sure I had the new phx_new 1.7.1 installer (this changes the generated project to include the hero icons) and generating a fresh project with the same name of your current. There are some new files you can wholesale copy in to your project.

Notes

• My update was made that much easier because I had already been using Elixir 1.14 and Tailwind. If those are new to your project this will have more to do.
• If I were updating a more significant project, I would treat the newer optional features of 1.7 (Removal of Views, Verified Routes) as later changes to be done in separate work. Getting to 1.7 without those is pretty painless, but when you do them all, it can get a bit heavy. (To keep using views look to adding {:phoenix_view, "~> 2.0"} to your dependency list.
• I did my best to update my own project to match the new generators as much as possible. This meant bring in some things like core components and hero icons I'm not using yet.
• Those hero icons were added in 1.7.1, and it took me a bit to realize I needed the 1.7.1 installer (I was using 1.7.0 at first).

[zorn]

TODO: Lookup what this means.

[zorn]

Was added in phoenixframework/phoenix#4677 and related to: phoenixframework/phoenix#4877

[zorn]

This was a new addition which is easy to miss. Seems like the preferred networking library for the default Swoosh integration. I'm not doing email currently, but I pulled it in to match the generator.

When adding it, I hit a bit of a dependency conflict with castore. I believe I resolved it by first unlocking castore (with mix deps.unlock castore) and then adding finch and running the normal deps.get.