Initially, this PR was intended to more clearly separate code between Krill
“business logic” – now bundled in a KrillManager –, and the HTTP server code
that serves the API. The former now lives in the server module, the latter
in the daemon module together with all the code to spin up a Krill daemon
driving the HTTP server.
However, along the way it turned into a complete redesign of how the HTTP
server code works. Request handling has been split into three stages that
forces implementers to check for permissions (or actively choose to not
check), and read the body (or check that there isn’t one). Dispatching of
the request has been restructured which should make it easier to follow what
goes on where.
This PR increases the minimum Rust version to 1.81.
