Add option to throttle and/or delay only specific request

[kokarn]

This would help out greatly with apps having multiple parts where you want to test out what happens if just one part is slow and/or unresponsive.

[mitchhentges]

Looks like hoxy already supports this, see request.slow() and response.slow()

[nerdbeere]

I like the idea. There should be a variety of things you should be able to do to a request/response:

• Throttling of requests
• Blocking requests with different HTTP responses
• Change the response body (https://github.com/james-proxy/james/issues/132)