Add inverse flag to external filter (for HGMD and ClinVar separately)

Description

Closes issues: Related issues:

Add inverse flag for external filter (both ClinVar and HGMD). This is done in response to user request to rescue variants that are DM/DM? in HGMD and not benign with more than one star in ClinVar.

Notes to reviewer

[Are there points in the code the reviewer needs to double check or where you would like advice?]

Type of change

• New feature
• Breaking change
• Bug fix
• Improvement

General

• Tests have been added that prove my fix is effective or that my feature works
• Related tests have been modified/removed

Hypothesis testing:

• Soak testing has been done
• Distribution between positive / negative cases has been checked

Database

• Includes changes to database schema
• Includes necessary database migrations

Configuration

• Includes changes to configuration
• Includes configuration migration instructions in documentation

General

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My branch has recently been updated with new changes in dev before this merge request
• I have made corresponding changes to the documentation