Draft: dns over https
Current WiP for DoH, on top of 1840-netmgr-tls-layer 'Big' things missing:
- Tests
- dig integration - dig should call isc_nm_doh_request()
- Listening - parsing the http server statement into isc_nm_listenhttp2 call
- Endpoint - paring the http endpoint statement into isc_nm_http_add_entpoint
- Reconfig -endpoint/listener removal
- Paring of 'GET' arguments (currently only POST requests are supported)