pgsql: Add description for new patterns supported in HBA and ident samp

Add description for new patterns supported in HBA and ident sample files

Support for regexps in database and role entries for pg_hba.conf has
been added in 8fea8683, and efb6f4a has extended support of pg-user in
pg_ident.conf, still both of them have missed a short description about
the new patterns supported in their respective sample files.

This commit closes the gap, by providing a short description of all the
new features supported for each entry type.

Reported-by: Pavel Luzanov
Reviewed-by: Jelte Fennema, Pavel Luzanov
Discussion: https://postgr.es/m/e495112d-8741-e651-64a2-ecb5728f1a56@postgrespro.ru

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/1b43743f1174a5b98f77c8090a89d829c2874441

Modified Files
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src/backend/libpq/pg_hba.conf.sample | 17 +++++++++--------
src/backend/libpq/pg_ident.conf.sample | 4 ++++
2 files changed, 13 insertions(+), 8 deletions(-)