DRAGEN: new module vc_hethom_ratio_metrics

[Just-Roma]

• This comment contains a description of changes (with reason)

• CHANGELOG.md has been updated

• There is example tool output for tools in the https://github.com/ewels/MultiQC_TestData repository or attached to this PR

• Code is tested and works locally (including with --lint flag)

• docs/README.md is updated with link to below

• docs/modulename.md is created

• Everything that can be represented with a plot instead of a table is a plot
  Only linegraphs are included by default. Bargraphs can be also quickly included by setting BARGRAPHS_ENABLED
  to True. The variable is in the vc_hethom_ratio_metrics.py file.

• Report sections have a description and help text (with self.add_section)

• Module does not do any significant computational work

This module can be considered experimental: it can work in 2 modes by setting the variable SQUASH_SECTIONS in vc_hethom_ratio_metrics.py to True/False.

1. If True, then only 1 section will be shown. Other sections can be chosen from a drop-list.
   This approach looks better but is unreliable, because hiding plots can break them when resizing/reloading html
   page. This bug seems to be common, at least the dragen_fastqc has the same issues.
2. If False, then all sections are shown. The mentioned bugs are absent, but html report looks worse.

Merging:

• merging this PR would require updates in dragen/dragen.py and multiqc/utils/search_patterns.yaml
  in PR1911, PR1912, PR1913, PR1914. But not in the dragen/utils.py, because it is the same. The main file must be also included, of course.