sqldb+config: validate maximum batch size config value

Now that the SQL query config values are configurable, we add some
validation to make sure that the user doesnt set a max batch size that
is larger than the limits for sqlite/postgres that have been determined
by the TestSQLSliceQueries test.

sqldb/paginate_test.go

@@ -281,11 +281,17 @@ func TestSQLSliceQueries(t *testing.T) {
 			break
 		}
 
-		x *= 10
+		// If it succeeded, we expect it to be under the maximum that
+		// we expect for this DB.
+		if isSQLite {
+			require.LessOrEqual(t, x, maxSQLiteBatchSize,
+				"SQLite should not exceed 32766 parameters")
+		} else {
+			require.LessOrEqual(t, x, maxPostgresBatchSize,
+				"Postgres should not exceed 65535 parameters")
+		}
 
-		// Just to make sure that the test doesn't carry on too long,
-		// we assert that we don't exceed a reasonable limit.
-		require.LessOrEqual(t, x, 100000)
+		x *= 10
 	}
 
 	// Now that we have found the limit that the raw query can handle, we