output_options document update

name: Bug report
about: output_options document update

Describe the bug
One of our astute users has pointed out that the "output_options" keyword contains
an underscore, whereas other configuration keywords use a hyphen. In the Kea ARM,
there are examples of usage of "output_options" and "output-options."

To Reproduce
Steps to reproduce the behaviour:
Start Kea with the following "loggers" definition

       "loggers": [ {
                "name": "kea-dhcp4",
                "output-options": [ { "output": "./kea-dhcp4.log" } ],
                "severity": "DEBUG",  "debug level": 99 }]

Kea will exit with the following error message:

DHCP4_INIT_FAIL failed to initialize Kea server: configuration error using file 'kea-template.json': kea-template.json:60.17-32: got unexpected keyword "output-options" in loggers map.

RT #22138