Add on to #181 Question clarification

[wendy-aw]

• Standardize Rishabh/clarify questions system prompt #181 changes across dialects
• Also removed 'MoM will always be zero for the first month that appears in your answer.' because the queries were modified such that mom is NULL in the first row. Not zero.
• Corrected a mini typo "Only included successful transactions" --> "Only include successful transactions"
• Remove consumer_div. schema name for MySQL, SQLite, BigQuery
• Clarify DDD question to return the average "Calculate the average DDD for each drug. Return the drug name and average DDD value." to match SQL.

Translation of the latest questions_gen to come in the next PR

[rishsriv]

Thank you for these changes, much appreciated!