Fix Discovery and Get API root Information endpoints

[seansica]

TAXII API Endpoints Fixes and Improvements

This PR addresses several issues in our TAXII API endpoints, improving compliance with the TAXII 2.1 specification and enhancing overall consistency.

Changes

1. Discovery Endpoint: Fixed the API root path issue.

   • Added a leading '/' to the relative path returned by the discovery endpoint.

2. Get API Root Information Endpoint: Corrected the version property.

   • Changed version: string to versions: string[] to correctly represent multiple supported versions.

3. Property Naming Convention: Implemented consistent snake_case for all properties.

   • Updated the following properties to use snake_case:
     • maxContentLength → max_content_length
     • canRead → can_read
     • canWrite → can_write

These changes improve our API's adherence to the TAXII 2.1 specification and provide a more consistent interface for our users.

Testing

• Verified that the discovery endpoint now returns the correct API root path with a leading '/'.
• Confirmed that the Get API Root Information endpoint returns versions as an array of strings.
• Tested all affected endpoints to ensure proper snake_case naming for all properties.