This splits the request handlers into two functions, one which is the actual
handler and one which is independent from the Grafana `ReqContext` object. This
is to make it easier to reuse the implementation in other code.
Part of the refactoring changes the functions which get query parameters from
the request to operate on a `url.Values` instead of the request object.
The change also makes the code consistently use `req.Form` instead of a
combination of `req.URL.Query()` and `req.Form`, though I have left
`api_ruler` as-is to avoid this PR growing too large.
Steve Simpson
a6ad2380bf