Add basic scATAC signac processing to cell-seek

[tovahmarkowitz]

Write scripts that will:

• Start with cellranger output from cell-seek for scATAC data
• Use scRNA scripts from cell-seek as a template
• Incorporate scATAC-specific processing steps including peak annotation, motif annotation, and pseudo-expression calculations.
• Identify appropriate reference packages for GRCh38-2020, GRCh38-2024, mm10-2020, GRCm39-2024
• Create merged object across multiple samples and repeat all steps