Axum middleware to rewrite a request such that a version prefix is added to the path. This is
based on a set of versions and an optional "x-api-version" custom HTTP header: if no such
header is present, the highest version is used. Yet this only applies to requests the URIs of
which pass a filter; others are not rewritten.
Custom HTTP header conveying the API version, which is expected to be a version designator
starting with 'v' followed by a number from 0..+99 without leading zero, e.g. v0.