fix(uploads): respect db engine spec's supports_multivalues_insert value for file uploads & enable multi-insert for MSSQL (#30222)

Co-authored-by: Ville Brofeldt <33317356+villebro@users.noreply.github.com>

superset/db_engine_specs/base.py

@@ -347,6 +347,7 @@ class BaseEngineSpec:  # pylint: disable=too-many-public-methods
     # Does database support join-free timeslot grouping
     time_groupby_inline = False
     limit_method = LimitMethod.FORCE_LIMIT
+    supports_multivalues_insert = False
     allows_joins = True
     allows_subqueries = True
     allows_alias_in_select = True
@@ -1283,9 +1284,11 @@ class BaseEngineSpec:  # pylint: disable=too-many-public-methods
             catalog=table.catalog,
             schema=table.schema,
         ) as engine:
-            if engine.dialect.supports_multivalues_insert:
+            if (
+                engine.dialect.supports_multivalues_insert
+                or cls.supports_multivalues_insert
+            ):
                 to_sql_kwargs["method"] = "multi"
-
             df.to_sql(con=engine, **to_sql_kwargs)
 
     @classmethod

superset/db_engine_specs/mssql.py

@@ -53,6 +53,7 @@ class MssqlEngineSpec(BaseEngineSpec):
     max_column_name_length = 128
     allows_cte_in_subquery = False
     allow_limit_clause = False
+    supports_multivalues_insert = True
 
     _time_grain_expressions = {
         None: "{col}",