[FR] unbound-control get_options

[popovr]

Current behavior
only one option which must be known in advance per request can be examined with 'unbound-control get_option option'

Describe the desired feature
It'd be usefull to be able to display via unbound-control all configuration options used by unbound process with values.
Values which differ from default should followed with default value in '()'.
Clauses like server, remote-control etc. may precede option names.

example:
unbound-control get_options
---skip---
server.ip-ratelimit-size: 16777216 (default: 4194304)
---skip---
remote-control.server-cert-file: "/etc/unbound/unbound_server.pem"
---skip---
dnstap.dnstap-enable: no
---skip---

Potential use-case
It's very helpfull to examine in one place all config options and values that unbound process is using.
At the moment the only way is to use 'get_option' for each single option which is not handy.