Don't require the query string to be UTF-8

[panicbit]

https://github.com/panicbit/northstar/blob/75a1cd1eb5e2720b247a802f2f8edcc67bf4a624/src/types/request.rs#L24-L33

[panicbit]

Notes:
PercentDecode<'a> implements Into<Cow<'a, [u8]>> and Iterator<Item = u8>.
The former would be preferred since it can save an allocation.