Generalize the GBT phase scan web interface

Description

This MR introduces a Radio button to select the type of GBT RX scan to be performed. At the moment, just the button for the one relative to the VFATs, but others can be implemented in the same fashion.

@lpetre , can you check that the RPC function is as desired? probably it needs to be modified.

Related Issue

How Has This Been Tested?

Types of changes

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

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.