Ensure cell type labels are retained when merging SCEs

[sjspielman]

When merging SCEs in scpcaTools::merge_sce_list(), we use a vector of colData columns to retain. Missing from this list are cell type annotation columns, but we would definitely like to retain them. We'll need to update the function, and its docs, accordingly.

[allyhawkins]

My understanding from DSTM was that we don't want to actually change the function, we just want to change the vector of column names that we provide when calling the function in scpca-nf. We will need to add the retain_coldata_cols argument here:
https://github.com/AlexsLemonade/scpca-nf/blob/f08ce452f95f88e169217c114aef1c1321a3688c/bin/merge_sces.R#L132

[sjspielman]

We will need to add the retain_coldata_cols argument here:

This won't work with our current implementation - I'm filing a PR for this fix now, eta 1 minute.

[sjspielman]

Indeed, this will happen in scpca-nf.