Control API: reload support.

Control API: reload support.

A new /control/config endpoint provides configuration reload function
with feedback returned to the user on the outcome.

Example:

$ curl 127.0.0.1:1234/1/control/config -X PATCH -v | jq
< HTTP/1.1 200 OK
< ...
<
{
  "logs": []
}

$ curl 127.0.0.1:1234/1/control/config -X PATCH -v | jq
< HTTP/1.1 422 Unprocessable Entity
< ...
<
{
  "logs": [
  "...: invalid number of arguments in \"listen\" directive"
  ]
}

Co-authored-by: Pavel Pautov <p.pautov@f5.com>