Normalize use of hyphen to underscore in API & LHR?

[paulirish]

In #6201 we found we have a problem with not-applicable. It can't be represented in proto enum as hyphens are no good but underscores are too.

We're seeing a similar issue with the API: ...&category=pwa&category=best_practices

In both cases, it looks like we can do a mapping to maintain our hyphen-first API, but it's overhead and technical debt that sucks to absorb. The other alternative is we switch to underscore for both of these.

This means all uses of best-practices (and not-applicable) in the LHR would switch to the underscore equivalent. And it'd also apply to CLI usage (--only-categories=best_practices) and LHR handling..

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TBH at this point I think I've talked myself out of the proposal. 🤣 Also if we're going hard on underscores then we might as well underscorify all the audit ids. Sounds exciting but not something to do right now. :)

Filing for posterity but for now it seems like we'll eat the debt of renaming underscore back to hyphen in our proto->json conversions.