Provide a way to disable SPA Mode

### Your use case

#### What would you like to do?

In certain deployments, the SPA mode does not make sense (For example, with MAS enabled, at the moment the SPA mode will just not work). We should have a config option to display a graceful failure mode when trying to access element call on SPA mode in this situation.

### Have you considered any alternatives?

_No response_

### Additional context

_No response_

Start by locating the SPA mode configuration and the entry point reached when accessing Element Call in SPA mode. Confirm how deployments with MAS enabled currently fail, then define the configuration behavior and the graceful failure state that would count as done.

Written by the indexing model from the issue text.