Added the functionality of assigning roles to users and few improvements

[sgremyachikh]

1. I would like to see the results of the deployment with details also in case of a cluster configuration change
2. I would like to see a list of users after deploying the database with the user roles, if they are specified
3. Added the functionality of assigning roles to users
4. I added an example in postgresql_cluster/vars/main.yml : we are adding the pg_monitor system role to the monitoring user

[vitabaks]

Thanks @sgremyachikh

[sgremyachikh]

Thank you for your job, it’s awesome solution to deploy ha Postgres cluster