reintroduce dependency on akka-http-cors (or pekko equivalent)

[pjfanning]

This project has a dependency on akka-http-cors. I have opened lomigmegard/akka-http-cors#258

I have the code updated to use Pekko in a temp fork. As a workaround, I can inline that code in this repo. When issue 258 is addressed, we can use that instead. This is better because we won't have to update our license to mention the inlined code.

[mdedetrich]

So a cors release has been made against pekko, see lomigmegard/akka-http-cors#258 (comment)

[mdedetrich]

@pjfanning Just letting you know that I am working on this now