Add regex capture and rename capture_bytes to capture

[XAMPPRocky]

This PR adds a regex capture strategy to the CaptureBytes filter, and renames it from CaptureBytes to capture, to better reflect the new Capture trait contract, where a capture strategy can return any valid metadata::Value instead of only Bytes. This also adds a /is_present extension metadata key which is appended ontop of whatever the metadata_key is, this will be useful in combination with #447 to allow to match on whether any successful capture occured, rather than only matching values.

[quilkin-bot]

Build Succeeded 🥳

Build Id: 86b76aaf-fbfd-4e1d-ae90-3aaa703cf09a

To build this version:

git fetch [email protected]:googleforgames/quilkin.git pull/458/head:pr_458 && git checkout pr_458
cargo build