Clarify how certain request headers in workers are added to the worker fetch API

### Existing documentation URL(s)

- https://developers.cloudflare.com/workers/runtime-apis/request/#incomingrequestcfproperties

### What changes are you suggesting?

Clarity on how additional headers are added to a request object when calling worker.fetch, such as x-fowarded-port, and how to remove them, or how there is not a way to remove them. A note on what request headers to worker.fetch can't be removed would be helpful.

### Additional information

For added context, there is this app https://adams-sublime-site.webflowtest.io/image-test/headers, that checks the headers. You will notice the x-forwarded-port header is included in the request. Haven't quite figured out how to remove this or if there is even a way to do that.