Update BeamSpotMon to use monitoring stream

Related MRs and Issues

Issue #100 (closed)

Description

Update the stream/routing bit over which BeamSpotMon runs to the new monitoring stream. Follows the instructions by @rmatev in the slides RM-RC-Monitoring under 'News' in the 09 May 2025 Run Meeting and the example for RecoMon from !620 (merged).