[Feature Request]: Add wellknown regex for URL encoded parameters

[weeco]

Feature description:

Protovalidate offers two wellknown regexes for header keys & values. It would be nice if it could be extended by one Regex that allows the character set for URL encoding only.

Problem it solves or use case:

It's common to use URL encoding for path parameters. If you want to setup a strict validation you are up to your own to define this regex.

Proposed implementation or solution:

I'm not entirely sure what the most correct Regex for this would be, but the RFC may help finding one: https://www.ietf.org/rfc/rfc3986.txt#:%7E:text=2.4.%20%20When%20to%20Encode%20or%20Decode%0A

Contribution:

It should be fairly simple to add, happy to do it as soon as we agreed on adding this and found a reasonable Regex.

Examples or references:

Additional context:

[rodaine]

Hey, @weeco! The KnownRegex are a holdover from the protoc-gen-validate days that we will likely deprecated prior to v1. Instead of putting this feature there, I'd say it's better suited as its own rule under the well_known oneof.