pgsql: Doc: add glossary term for "auxiliary process"

Doc: add glossary term for "auxiliary process"

Add entries for existing processes not documented, too, and adjust
existing definitions for consistency.

Per question from Bharath Rupireddy.

Author: Justin Pryzby <pryzby@telsasoft.com>
Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/CALj2ACVpYCT0M+k8zqrAa4ZQZV+ce5s6G=yajwoS1m=h-jj8NQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d3014fff4cd4dcaf4b2764d96ad038f3be7413b0

Modified Files
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doc/src/sgml/glossary.sgml | 118 +++++++++++++++++++++++++++++++++++++++------
src/include/miscadmin.h    |   2 +
2 files changed, 106 insertions(+), 14 deletions(-)