Add function to create total CNV column

[sjspielman]

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Part of #1143

Describe the goals of the changes to the analysis module.

We have this function in the exploratory notebooks in the infercnv-consensus-cell-type module appearing in multiple exploratory notebooks:

OpenScPCA-analysis/analyses/infercnv-consensus-cell-type/exploratory-notebooks/02_ewings-reference-cnv.Rmd

Lines 34 to 62 in 47d2188

	```{r}
	prepare_cnv_df <- function(infercnv_tsv) {
	infercnv_df <- readr::read_tsv(infercnv_tsv)
	infercnv_metadata_df <- infercnv_df |>
	dplyr::select(
	-starts_with("has_"),
	-starts_with("proportion_"),
	-starts_with("top_")
	) |>
	dplyr::mutate(cell_group = stringr::str_split_i(subcluster, "_", 1))
	infercnv_df |>
	tidyr::pivot_longer(
	starts_with("has_cnv_"),
	names_to = "chr",
	values_to = "cnv"
	) |>
	# sum all values for each
	dplyr::group_by(cell_id) |>
	dplyr::summarize(total_cnv_per_cell = sum(cnv)) |>
	dplyr::ungroup() |>
	# bring back metadata
	dplyr::inner_join(
	infercnv_metadata_df,
	by = "cell_id"
	)
	}
	```

When we return to working on this module for neuroblastoma samples, we should move this function into its own utils file to keep things modular since we anticipate using it more in the future.

What will your pull request contain?

New utils file with functions that are imported in relevant notebooks

Will you require additional software beyond what is already in the analysis module?

No

Will you require different computational resources beyond what the analysis module already uses?

No

If known, when do you expect to file the pull request?

No response