Create API endpoint to search custom fields

[jasonwuwrf]

Is your feature request related to a problem? Please describe.
Create endpoint to search for custom fields in use on IP Addresses, and for specific addresses.
/api/my_app/addresses/search_custom_field/{custom_FieldName}/{custom_FieldValue}

Describe the solution you'd like
API endpoint: /api/my_app/addresses/search_custom_field/custom_loggingHighImpactSystem/

Describe alternatives you've considered
N/A

Describe how the feature would benefit other users
Extends capabilities to find IP addresses that have your custom values set on them.

[jasonwuwrf]

I will be submitting a pull request on this