Add session_role to postgresql modules (#43650)

* Allow session_role to be set for PostgreSQL

By implementing session_role it becomes possible to run the specific
PostgreSQL commands as a different role.
The usecase that is immediately served by this, is the one that one
ansible playbook can be shared by multiple users, which all have
their
own PostgreSQL login_user. They do not need to share login
credentials,
as they can share the role within the PostgreSQL database.

The following example may give some insight:

$ psql -U jdoe -X -d postgres

postgres=> CREATE DATABASE abc;
ERROR:  permission denied to create database
postgres=> set role postgres;
SET
postgres=# CREATE DATABASE abc;
CREATE DATABASE

fixes #43592

* Tests for session_role in PostgreSQL

* Bump version_added for session_role feature

* Remove explicit encrypted parameter from tests

test/integration/targets/postgresql/defaults/main.yml

@@ -6,3 +6,5 @@ db_user2: 'ansible_db_user2'
 db_user3: 'ansible_db_user3'
 
 tmp_dir: '/tmp'
+db_session_role1: 'session_role1'
+db_session_role2: 'session_role2'