Adding entity resolver fix for entityResolver(multi: true) directive

[RyanMcCabe-catapult]

A fix for the issue described in issue 3160. If the multi entity is used in any other resolver the error would always be thrown, now it is just skipped. The multi entity resolver has the directive set and runs it, the other resolvers don't have it set so it gets skipped and works as expected.

I have:

• Added tests covering the bug / feature (see testing)
• Updated any relevant documentation (see docs)

[coveralls]

coverage: 56.722% (+0.05%) from 56.668%
when pulling 07d9d54 on RyanMcCabe-catapult:issue-3160/entity-resolver-fix
into cf42b25 on 99designs:master.

[clayne11]

@RyanMcCabe-catapult thanks for trying to fix this. This isn't the best way to implement this.

Inside of plugin/federation.go you should add entityResolver to the skipRuntime config. That way we don't have to add one-off changes to the shared template itself.