Add EncounterNumber Index to HSAA.Encounter

Adding an index on EncounterNumber in HSAA.Encounter will significantly enhance query performance by reducing full table scans, optimizing joins, and accelerating data retrieval for reporting and analytics. Many reports and queries rely on filtering or joining by EncounterNumber, and without an index, these operations require scanning large volumes of data, leading to slower response times and increased system load. By indexing this column, queries can leverage efficient lookups, reducing execution time, minimizing database contention, and improving overall system performance, especially when handling high volumes of concurrent requests.