new module: gatk4/concordance

[kubranarci]

Is there an existing module for this?

• I have searched for the existing module

Is there an open PR for this?

• I have searched for existing PRs

Is there an open issue for this?

• I have searched for existing issues

Further Information

This new module will be used part of nf-core/variantbenchmarking

Are you going to work on this?

• If I'm planning to work on this module, I added myself to the Assignees to facilitate tracking who is working on the module