Add support for ansible-playbook serial > 1 (manage multiple hosts at a time)

[georgelupu]

At the moment (grafana-ansible-collection v2.2.5), it is not possible to run ansible-playbook in parallel on 2 (or more) hosts and specify different {{ grafana_agent_version }}.

Steps to reproduce:

1. Crate an inventory file with 2 hosts - for example:
   all:
   children:
   my_db:
   children:
   db1:
   hosts:
   10.10.10.10:
   db2:
   hosts:
   10.10.11.10:
2. set serial to 2 (or 100%) in your ansible playbook yaml file.
3. set {{ grafana_agent_version }} variable to different versions in the respective db1 and db2 group_vars files.
4. run ansible-playbook and notice how:
   4.1) two distinct grafana-agent_*.zip files are downloaded on the controller host in {{ grafana_agent_local_tmp_dir }} for each respective versions.
   4.2) in the same {{ grafana_agent_local_tmp_dir }} on the controller host, unzip task will run twice. Destination file has the same name, so the last unzip for ver B will override the previous unzip for ver A.
   4.3) the incorrect version grafana-agent unzipped binary will get propagated to one of the remote hosts.

Workaround until a fix is provided:

• Run ansible-playbook with serial=1, one node at a time.