Postgres parser fails on schema-qualified `COMMENT ON TYPE` and `COMMENT ON VIEW`

[devfros]

First, thank you for maintaining sqlglot. It has been very useful for my personal project.

Problem

sqlglot fails to parse valid PostgreSQL COMMENT ON statements when the target is schema-qualified for some object kinds, notably TYPE and VIEW.

Reproduction

from sqlglot import Dialects, parse

cases = [
    "COMMENT ON TYPE mood IS 'x';",
    "COMMENT ON TYPE foo.mood IS 'x';",
    "COMMENT ON VIEW foo.bat IS 'x';",
    "COMMENT ON TABLE foo.bar IS 'x';",
    "COMMENT ON COLUMN foo.bar.baz IS 'x';",
]

for sql in cases:
    print(sql)
    print(parse(sql, dialect=Dialects.POSTGRES))

ParseError: Required keyword: 'expression' missing for <class 'sqlglot.expressions.ddl.Comment'>.

[devfros]

I can make a PR

[geooo109]

@devfros feel free making a PR, happy to review.