Fix PARSE_BADFILE default filename format in documentation

[igi-i]

I found a discrepancy between the official pg_bulkload documentation and the actual behavior regarding the default output filename of PARSE_BADFILE.

In my environment (PostgreSQL 18.3 + pg_bulkload 3.1.23), the generated filename uses:

.prs.
However, the official documentation states:
.bad.

This patch updates both the Japanese and English documentation to match the actual behavior.