records: allow bulk subscription to record update notifications for analysis framework authors

[GraemeWatt]

Logged-in users can subscribe to individual records simply by clicking the "Watch Record" button on each record, then they will receive an email notification if a new version of that record is finalised. After my talk at the Reinterpretation & OpenMAPP mini-workshop last week, there was some discussion (with @sabinekraml) of how analysis framework authors could receive such notifications automatically without needing to subscribe to individual records themselves. We could extend the ANALYSIS_ENDPOINTS (currently only implemented for Rivet and MadAnalysis 5) to take an optional argument like subscribe_user_id with the user ID of the analysis framework author who wishes to receive notifications. Then the update_analyses function could automatically subscribe to all records listed in the analyses.json file if the user given by subscribe_user_id is not already subscribed.