Ignore not configured flags in json file

[kungf]

What type of PR is this?

• bug

What this PR does / why we need it:

Flags has default value, no need config every flag in config file

Which issue(s) this PR fixes:

(REQUIRED)

Special notes for your reviewer:

(fill-in or delete this section)

Testing

(fill-in or delete this section)

Release Notes

(REQUIRED)

[kungf]

hi, @rliebz @saschagrunert, who can have a review please.

[dearchap]

Hmm actually isc.IsSet checks if the value is defined in the key or not so we dont need this feature.