Integrate gnomAD v4 frequencies

[holtgrewe]

Is your feature request related to a problem? Please describe. gnomAD v4 has updated frequencies. As v4 is larger than v2/v3 combined, it is considered more reliable.

Describe the solution you'd like Provide gnomAD v4 frequencies.

Describe alternatives you've considered N/A

Additional context

• https://github.com/bihealth/reev/issues/235

[holtgrewe]

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