Improve getTemporaryToken logic

[ptbrowne]

At the moment, we need to have logic in harvest code to know which budget insight endpoint to target. This is brittle since we need to update the code if the endpoint changes, and we can have a discrepancy between the endpoint used by the konnector to create the token, and the endpoint used by the front. See #1225 for a fix that is needed.

What would be better would be that the konnector sends the endpoint + the token when the front runs getTemporaryToken. This way we can remove the endpoint logic from harvest.

Also, it would be better suited to support budget-insight for self hosted Cozys / Gandi cozys (for which domain is not known in advance).