GIE support profile() and explain() step?

**Is your feature request related to a problem? Please describe.**
As we all know, tinkerpop supports two steps: profile() and explain(). You can mainly see the execution plan and performance tuning in daily life.

Start by locating the GIE entry points for the profile() and explain() steps and reviewing how existing query steps are handled. Determine the intended execution-plan and performance-tuning behavior before implementation; done means both steps are supported in GIE with documented behavior and validation.

Written by the indexing model from the issue text.