feat: generate alignment pileups

[deliaBlue]

This PR closes #4 .

The changes in this PR are:

• Add the script that generates the ASCII-style pileups
• Add the workflow that generates the pileups (pileup.smk)
• Add a new function in the common.smk to generate an empty BED file if not provided by the user
• Add the new workflow and its output files in the main Snakefile
• Add the pileups parameters in the config_template.yaml, config_schema.json and test/config.yaml files
• Add the BED files with the regions of interest as a test input file
• Document the new workflow in the main README, the configuration README and in the pipeline_documentation.md
• Update the expected output and the rule graph

[uniqueg]

Looks good. Few minor issues

[uniqueg]

Getting there :)

[uniqueg]

Thanks :)