[COMMITTERS] pgsql: Document current_role.

Document current_role.

This system function has been there a very long time, but somehow escaped
being listed in func.sgml.

Fabien Coelho and Tom Lane

Discussion: https://postgr.es/m/alpine.DEB.2.20.1705061027580.3896@lancre

Branch
------
REL9_3_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/babf8f1c3825fdcd416caa90e51af360a613ea32

Modified Files
--------------
doc/src/sgml/func.sgml | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)