Ignore Introspection queries in QueryComplexity rule

[ruudk]

Followup from https://github.com/webonyx/graphql-php/discussions/1203

The QueryComplexity rule should ignore introspection query. This way you can set the max query complexity very low and still allow introspections to happen.

Introspection has a complexity of around 181.

[kinimodmeyer]

In regards to https://github.com/webonyx/graphql-php/issues/1207 i guess i would also like to calculate the introspection queries as they can produce a significant load.

Maybe we can implement this feature here in that way, that we have the option enable/disable the exclude.

Thanks!