Add the ability to set a repositoryHost for form validation

[Jonesy]

Description

Fixes the URL form validation aspect of a code request and also adds a new feature to declare a repositoryHost variable so source repositories can be restricted to a specific origin.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Documentation (non-breaking change with enhancements to documentation)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the CONTRIBUTING doc
• I have checked that unit tests pass locally with my changes
• [x I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments