Improvements and simplification of the cluster scaling process.

[vitabaks]

Playbook add_pgnode.yml

• Previously, you had to add a new node yourself to the pg_hba.conf file on all nodes of existing cluster before adding a new node to the cluster. Now it will be done automatically.

• Previously, it was necessary to add a new node (which you want to add to existing cluster) in the [replica] group and at the same time remove other nodes from the replica group from inventory in order to add_pgnode.yml playbook was executed specifically for the new server.
  Now you do not need to do this, you just need to specify the variable new_node=true for the server that you are adding to the cluster and the playbook will be executed only on this server.

Playbook add_balancer.yml

• Previously, configuration files were copied from the server from the master group. This is not very convenient, for example, when the load balancers are placed on separate servers. Now the files are copied from the first server specified in the inventory file in the balancers group.
• Specify the variable new_node=true for the balancer server that you are adding to the cluster and the playbook will be executed only on this server.