fix(terraform): Security group attached to an Elastic DocumentDB cluster is not recognized by check CKV2_AWS_5

[bhean]

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Description

Include Elastic DocumentDB as a valid associated resource for an aws_security_group for graph check CKV2_AWS_5

Fixes #6686

Checklist:

• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [x] I have added tests that prove my feature, policy, or fix is effective and works
• [x] New and existing tests pass locally with my changes