BUG #17775: Clarify default value for HEADER argument in documentation

The following bug has been logged on the website:

Bug reference:      17775
Logged by:          Felix Sperling
Email address:      fsperling@salesforce.com
PostgreSQL version: 15.1
Operating system:   any
Description:

Hello,

I would like to ask for clarification in the documentation regarding the
COPY command and what the default value is for the HEADER argument.
I'm assuming the default is false as nothing else is mentioned but it would
be nice to have that more explicit in the docs.

https://www.postgresql.org/docs/15/sql-copy.html

Thanks,
Felix