Remove unnecessary strict enums on filterconfig schema

Description

Closes issues: Related issues:

Removed restrictions on filterconfigs schema for frequency group names. This is checked against the app configuration, so do not need these restrictions here. There could be a case for adding restrictions on the application config for frequency annotation coming from anno (GNOMAD_EXOMES/GNOMAD_GENOMES subpopulations), but that has not been implemented here.

Notes to reviewer

Type of change

Application (affects UI or general functionality):

• New feature
• Bug fix
• Improvement

Ops / admin / CI related only (not impacting users):

• New feature
• Bug fix
• Improvement

Tests

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

Merge checklist

• Self-review of code performed
• Feature review against specification (if applicable)
• Need for documentation has been evaluated and, if necessary, updated
• Code and implementation is reviewed by other core developer (all changes, inc. changes based on initial review)