Extend protection against potential XSS vulnerability

See SI-12 for original issue and steps to reproduce.

Extend URL validation introduced in SI-12 that prevents execution of malicious URLs to prevent saving potentially malicious URL strings.

Scope: 

• Context: Create or edit dashboard widgets with URL fields
• Applies to: URL links defined with a protocol identifier
• Does not apply to: URL link strings defined without a protocol identifier 

Related Prior Work: 

• https://github.com/folio-org/ui-dashboard/pull/224

Acceptance Criteria:

• Given a string is entered in the URL link field of a dashboard widget
• When a user attempts to save the widget
  • And the string is prefixed with a protocol identifier other than `https` or `http`
• Then do not save the record
  • And return the user to the widget edit/create screen 
  • And highlight the invalid field with
    • error styling
    • error message: "Please enter a valid URL (starts with \"https://\", \"http://\" or \"/\" and doesn't contain special characters not allowed in URLs)"