Add Pass & Drop filters, Refactor Match config

[XAMPPRocky]

This adds simple "pass" and "drop" filters, that either always allow a packet to pass, or always drop a packet. These filters aren't useful on their own, but become useful when used in combination with conditional flow filters like Match (#447).

closes #454

[markmandel]

Only question I have: Did we want to include the documentation with these Filters in this PR, or should it come as a separate? (if separate, let's track that in an issue, so we don't forget).

Otherwise, LGTM!

[XAMPPRocky]

I've added documentation, and I've also refactored a small bit of Matches, I've now renamed it to Match, and I've updated it from having special cased Pass and Drop branches in its configuration, if you want to drop or pass a packet, you should use the Pass and Drop filters. This simplifies some of the configuration.

@markmandel Would nice to get this in the next release, so that it's not technically a breaking change.

[quilkin-bot]

Build Succeeded 🥳

Build Id: 275f4fa7-dea0-4a5c-bbf0-65badb82f000

To build this version:

git fetch git@github.com:googleforgames/quilkin.git pull/472/head:pr_472 && git checkout pr_472
cargo build

[markmandel]

(non blocking): I assume the r# is because match is a keyword?