[Postgres] (NTILE) support

[eXigentCoder]

Describe the bug
When trying to parse a postgresql statement with an NTILE in it we are getting the following error:

"Expected \",\", \"--\", \"/*\", \";\", \"FROM\", \"GROUP\", \"HAVING\", \"INTO\", \"LIMIT\", \"OFFSET\", \"ORDER\", \"UNION\", \"WHERE\", \"WINDOW\", [ \\t\\n\\r], or end of input but \"(\" found."

PostgreSQL description of NTILE

Database Engine
PostgreSQL.

To Reproduce
-the SQL that be parsed

  SELECT  name,
                  amount,
                  NTILE (3) OVER (
                      ORDER BY amount
                  ) ntile,
                  unset(_id)
          FROM function-test-data
          WHERE testId='bugfix.ntile.case1'

-the node-sql-parser version
4.6.5
-the node version
v14.21.1

Expected behavior
To get back a parsed AST

Screenshots
N/A

Additional context
N/A