Add TOP to select clause modifiers for redshift dialect

Fixes #3531

src/sqlfluff/dialects/dialect_redshift.py

@@ -2258,3 +2258,11 @@ class CallStatementSegment(BaseSegment):
         "CALL",
         Ref("FunctionSegment"),
     )
+
+
+class SelectClauseModifierSegment(postgres.SelectClauseModifierSegment):
+    """Things that come after SELECT but before the columns."""
+
+    match_grammar = postgres.SelectClauseModifierSegment.match_grammar.copy(
+        insert=[Sequence("TOP", Ref("NumericLiteralSegment"))],
+    )

test/fixtures/dialects/redshift/select_top.sql

@@ -0,0 +1 @@
+SELECT TOP 10 example_value_col FROM example_schema.some_table ORDER BY example_value_col;

test/fixtures/dialects/redshift/select_top.yml

@@ -0,0 +1,32 @@
+# YML test files are auto-generated from SQL files and should not be edited by
+# hand. To help enforce this, the "hash" field in the file must match a hash
+# computed by SQLFluff when running the tests. Please run
+# `python test/generate_parse_fixture_yml.py`  to generate them after adding or
+# altering SQL files.
+_hash: 894b302c1b6551a0d3ce2623548d2284bce4dc09e1b2b5cc3cd7bc3ec737b7e4
+file:
+  statement:
+    select_statement:
+      select_clause:
+        keyword: SELECT
+        select_clause_modifier:
+          keyword: TOP
+          literal: '10'
+        select_clause_element:
+          column_reference:
+            identifier: example_value_col
+      from_clause:
+        keyword: FROM
+        from_expression:
+          from_expression_element:
+            table_expression:
+              table_reference:
+              - identifier: example_schema
+              - dot: .
+              - identifier: some_table
+      orderby_clause:
+      - keyword: ORDER
+      - keyword: BY
+      - column_reference:
+          identifier: example_value_col
+  statement_terminator: ;