Update Blocking Monitoring.sql

[Imran-imtiaz48]

Comments & Documentation: Clearer instructions and links. Validation: Script checks if sp_WhoIsActive is installed. Output Columns: No spaces in @output_column_list to avoid runtime errors. Error Handling: Use of IF OBJECT_ID to prevent script errors. Formatting: Improved readability via indentation and sectioning. CROSS APPLY: Use r.sql_handle instead of r.plan_handle for sys.dm_exec_sql_text, which is the correct parameter.