Integrating metadata lists in configuration

[XAMPPRocky]

ooooh yeah, I see your point. 👍🏻 Oh that's load of fun. Prefix and Suffix are checking for a match just by the nature of checking if there is enough data to actually grab. Excellent point, I didn't think of it that way.

Now whether this behaviour is desirable is a different story. I agree that this filter should probably only be capturing, and make it configurable as to whether it drops on failing captures. I can add that change to this PR if you agree.

I would absolutely be happy for this addition. I'll leave it up to you if you want to do it in this PR, or we can create an issue and track it as a separate unit of work.

Originally posted by @markmandel in #458 (comment)

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I want to expand on this idea a bit, and think we should think about what would be to incorporate metadata lists hollistically into Quilkin. While we could add an option to just token_router, I think we should consider having some kind of indexing syntax for metadata in the configuration, would be more much flexible and useful for anything else we add. For example, it could be used add support for map types. That can be used for parser filters to provide more rich information (e.g. capturing the version and the contents as metadata). For example; with the regex filter this would allow for named capture groups.