feat(copy): support copy from 'x.csv' grammar

[infdahai]

issue: #404

1. just add parser's support for this statement.

the output of binder_test

Exception Type :: Not implemented
Message :: T_CopyStmt
unknown file: Failure
C++ exception with description "T_CopyStmt" thrown in the test body.

[skyzh]

I didn't realize copy from / copy to are not standard Postgres SQL. But given we are actually using DuckDB's parser, I'd prefer keep this repo as-is DuckDB. Do you know which commit you are using from DuckDB?

[infdahai]

I will test it in the latest branch after a few days. I forgot the origin commit.