Extended AI feature usage tracking in GONG_USAGE table and __NEXT field removal

Multiple new metrics added to the GONG_USAGE table to track AI feature adoption:

• ASSISTANT_CHATS: Number of chats started by a user on a specific date
• THEME_SPOTTER_ANALYSIS_GENERATED: Number of AI Theme Spotter analyses generated by a user
• THEME_SPOTTER_ANALYSIS_USED: Number of AI Theme Spotter analyses where the user performed an action
• MEETING_PREPARATION_USED: Number of meetings for which a user used meeting preparation
• PRACTICES_STARTED: Number of AI Trainer practices started by a user
• TRAININGS_SUBMITTED: Number of AI Trainer trainings submitted by a user
• TRAININGS_STARTED: Number of AI Trainer trainings started by a user

__NEXT fields have been removed from all Gong data cloud tables.