Add behavioral testing for creating new posts

[jazzsequence]

In order to test issues like the one resolved in #164, we need to have a way to create new posts as part of automated testing. In this context, we need to be able to walk through the steps of creating a new post such that the javascript and API requests are in use (e.g. through a browser interface) when the post is created so we can identify when those api endpoints are failing.

I believe this is possible to do with Playwright, since it fires up a browser to run its tests, but would need to investigate further for implementation.