[#75962980] Check URL is blacklisted when reading from queue 

Check if a URL is blacklisted as we read it from the RabbitMQ queue to
prevent us from crawling blacklisted URLs.

Previously we would only check URLs that were extracted from a crawled
HTML document.
You can change this out to use the `Eventually` function as used in #46.

```go
Expect(len(outbound)).To(Equal(1))
Eventually(outbound).Should(HaveLen(0))
```