Allow for data key in Introspection diff

[tvvignesh]

Description

Addressing feedback from @AllexVeldman here: https://github.com/kamilkisiela/graphql-inspector/pull/2054#discussion_r774396413 with respect to allowing optional data key during introspection.

Fixes https://github.com/kamilkisiela/graphql-inspector/pull/2054#discussion_r774396413

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

Checklist:

• [x] I have followed the CONTRIBUTING doc and the style guidelines of this project
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [ ] Any dependent changes have been merged and published in downstream modules

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[AllexVeldman]

@kamilkisiela Is there anything we need to do to advance this PR?