feat: support password protected posts

[dustin-jw]

Description

This work adds the required logic and templates to support password protected posts and pages. The newly established pattern is to use the render_with_password_protection function on any single post page, which will render the single-password.twig template if a password is required. For listing pages, a filter was added to set has_password to true for non-admin queries.

Closes #48

To Validate

1. Make sure all PR Checks have passed
2. Pull down this branch
3. Run npm start
4. Add enough varied test posts to validate when they are or aren't being shown in listing pages
5. In the WordPress editor for one or more posts, set the visibility to "Password protected", and publish the post
6. View the post and confirm that you need to enter a password to see the page
7. Do the same for a Page, such as the "Sample page" that's added when you first initialize WordPress
8. Check the listing pages to make sure the password protected posts aren't shown, including:
   1. The home page
   2. The search page (?s=search+term)
   3. Category pages (?cat=1)
9. Change the password protected posts to be "Public" and confirm that they don't require passwords on the pages themselves and that they are shown in listing pages

[dustin-jw]

Removing these wasn't strictly necessary, but these variables weren't used anywhere from what I could tell.

[rise-erpelding]

Works great! I can set a password on a post and not be able to see it in the listing/search for it, if given the url I can't see the content without the correct password, and removing this setting also works as expected (and vice versa). 🏆