This commit adds an audit user to the postgresql database which
will have only SELECT privileges on the postgresql database tables.
This is accomplished by setting up audit user creation parameters
in the Patroni bootstrap environment settings, according to (1).
(1) https://patroni.readthedocs.io/en/latest/ENVIRONMENT.html
Change-Id: Idf1cd90b5d093f12fa4a3c5c794d4b5bbc6c8831