Add support for filtering, modifying and replaying saved requests

[forgedhallpass]

Since we already support saving requests into files, it would be nice if we would also enable post-processing/filtering of those requests.

Use-case:

1. automatically/manually crawl an application and proxy the requests through proxify
2. look at the saved requests saved, notice some interesting things/patterns
3. filter the existing local requests using your observations (e.g. consider requests only targeting a specific URL path like /api/v1/)
4. realize it would make sense to change the session id (e.g. admin vs user session to look for authorization issues)
5. replay the filtered and modified local requests against the target, or potentially even against another similar targets
6. pipe it through httpx and filter only requests that returned 200 OK

Note: merging current reply in proxify will be handled in a follow-up ticket

[laluka]

Definitely a needed feature, it would be awesome to be able to take a raw file and replay it, or submit it many times with various modification (burp-intruder-like feature with some extra scripting) !

[mohakim]

+1 on this. Could be super useful. Burp proxy history and repeater equivalent. mitmproxy also supports this I think.