pgsql: Doc: minor improvements to SNI documentation.

Doc: minor improvements to SNI documentation.

My attention was drawn to this new documentation by overlength-line
complaints in the PDF docs builds: the synopsis for hostname lines was
too wide.  I initially thought of shortening the parameter names to
fit, but it turns out that adding <optional> markup is enough to
persuade DocBook to break the line, and that seems more helpful
anyway.

While here, I couldn't resist some copy-editing, mostly being
consistent about whether to use Oxford commas or not.  The biggest
change was to re-order the entries in the hostname-values table to
match the running text.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7c08a7e809721212b0c2b694cd19bd4379b8974f

Modified Files
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doc/src/sgml/runtime.sgml | 45 +++++++++++++++++++++++----------------------
1 file changed, 23 insertions(+), 22 deletions(-)