Add HDL h2 and rg modules

[lyh970817]

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HDL estimates SNP heritability and pairwise genetic correlation from GWAS summary statistics.
This PR upstreams hdl/h2 and hdl/rg together so nf-core/modules covers both HDL entry points with their shared reference-panel input contract.

The required shared HDL fixtures are provided in the companion nf-core/test-datasets PR: nf-core/test-datasets#1932