feat: Allow reading csv files without a header

[scsmithr]

> select * from read_csv('./testdata/csv/headerless.csv', header => 'false');
┌──────────┬──────────┬──────────┬──────────┐
│ column_1 │ column_2 │ column_3 │ column_4 │
│       ── │ ──       │ ──       │       ── │
│    Int64 │ Utf8     │ Utf8     │  Float64 │
╞══════════╪══════════╪══════════╪══════════╡
│        1 │ hello    │ world    │  3.90000 │
│        2 │ HELLO    │ WORLD    │  4.90000 │
└──────────┴──────────┴──────────┴──────────┘

Also does things with the signature. Closes #2375