Add ignore list to no-unused-fields rule

[maciesielka]

Is your feature request related to a problem? Please describe.

The no-unused-fields rule is a great way to avoid bloat in my schema, but I'm willing to accept that bloat in some cases. For example, I'm not worried if I don't request all the relay pagination fields for every connection exposed in my schema. Currently, though, that's a dealbreaker preventing me from using this rule.

Describe the solution you'd like

Any configuration option to provide a list of fields that are allowed to be unused. I'm not particularly wedded to any format for that configuration, but I'll provide a PR shortly that showcases one option. see PR here with one possible option.

Additional context

n/a