libpq-oauth: Print libcurl version with OAUTHDEBUG_UNSAFE_TRACE

libpq-oauth: Print libcurl version with OAUTHDEBUG_UNSAFE_TRACE

When debugging an OAuth trace, it's helpful to know what version of Curl
is in use. The SSL library that Curl is using (which may not be the one
in use by libpq) is also relevant, and it's just as easy to get, so
print that too.

This is being added post-feature-freeze, with RMT approval, in order to
fix some tests in the face of an upstream Curl regression. A subsequent
commit will make use of it in oauth_validator. Backpatch to 18 as well.

Tested-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAOYmi%2B%3DkP86t%2BZFFXNQ9G6K4ht7utdmB%3DCzhP%3DZ2wvuBymOTtQ%40mail.gmail.com
Backpatch-through: 18