Use Go 1.22 HTTP router in fake API

[okokes-akamai]

General:

The Fake API has long been a pain to manage - the routing mechanism within it is bunch of switch statements nested in yet another layer of switch statements, string.Splits, regexps etc.

I have not refactored the endpoints' implementations, just moved them to the new muxer.

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[avestuk]

Excellent improvement

[tchinmai7]

Amazing QOL improvement!