Add optional query text and plan collection flags (#337)

[erikdarlingdata]

Summary

• Adds collect_query and collect_plan bit columns to config.collection_schedule (NOT NULL, DEFAULT 1)
• Users can set either flag to 0 per-collector to disable text/plan storage and reduce data volume
• Collectors 08 (query_stats), 09 (query_store), 10 (procedure_stats) read the flags and return NULL when disabled
• Includes idempotent ALTER TABLE with named constraints for existing installations

Test plan

• Clean install on sql2016 — all 51 scripts pass, 46 collectors succeed
• New columns default to 1 on all schedule rows
• With defaults (1): query_text and query_plan_text populated correctly
• With flags set to 0: query_text and query_plan_text are NULL in new rows

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