Refactor from using `loadByProperties` to using an entity query.
`loadByProperties` doesn't allow for passing multiple values for a
single property such as multiple tags to compare against, and also means
that removing the current node can be done in the query rather than
filtering it out of the Collection.
This might also be a more performant solution if we can do the grouping
and sorting of the results in the query rather than needing to perform
additional steps on the result.
References #3
Add the initial code for specifying a blog post and returning related
posts. This includes adding a repository for related posts, and adding
it as a service within the `opdavies_blog` module.
References #3
