Add configuration for EBRAINS authentication token in tvb-web framework

To use the Siibra Creator page and extract connectivities from the KG, an EBRAINS authentication token is needed.

For the TVB Web GUI, there should be a new field in the Siibra Creator page, where the user can enter their token. This token should be saved as a User preference, such that when the user reopens the same creator page, the previous value is shown directly.
With every operation launch this UserPreference should be updated in DB, to be the latest for the next runs.

This new input field should be required.