Support `flattenFragments` for `validate` command's max depth determination

[n1ru4l]

We currently assume flattenFragments set to true for the audit command, but assume flattenFragments set to false for the validate command.

The reason for this is that the validate command was present before introducing the audit command and for some reason we re-implemented the depth count algorithm from scratch for the latter command based on the graphql-armor implementation (see graphql-armor source code).

To fix this inconsistency we should:

1. Use the same implementation for both the audit and validate command
2. Add a parameter for customizing how fragments should be treated (e.g. --max-depth-flattenfragments)

By default it makes more sense to have flattenFragments to be set to true as they do not really introduce depth for the execution compared to e.g. a selection set.