Document default values for pgoutput options + fix missing initialization for "origin"

Hi,

The pgoutput plugin options are documented in the logical streaming
replication protocol, but their default values are not mentioned.
This can be inconvenient for users - for example, when using pg_recvlogical
with pgoutput plugin and needing to know the default behavior of each option.
https://www.postgresql.org/docs/devel/protocol-logical-replication.html

I'd like to propose adding the default values to the documentation to
improve clarity and usability. Patch attached (0001 patch).

While working on this, I also noticed that although most optional parameters
(like "binary") are explicitly initialized in parse_output_parameters(),
the "origin" parameter is not. Its value (PGOutputData->publish_no_origin)
is implicitly set to false due to zero-initialization, but unlike other
parameters, it lacks an explicit default assignment.

To ensure consistency and make the behavior clearer, I propose explicitly
initializing the "origin" parameter as well. A patch for this is also attached
(0002 patch).

Thoughts?

Regards,

--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION