Add support for ansible 2.20.x

[sflotron]

Could you please add support for ansible 2.19.3 ? Currently we have this warning when runnig the latest version of the collection

[WARNING]: Collection prometheus.prometheus does not support Ansible version 2.19.3

Thanks a lot in advance for your answers

[pierresebastien]

PR #650 is required for Ansible 2.19 on system using APT as package manager

[hollow]

This should now be changed to support Ansible 2.20.x; currently unusable because of #651 breaking all playbook runs.

[sflotron]

Do you have some updates about supporting ansible 2.20.x ?

[simonLeary42]

This PR has the tests passing for 2.19.x: #727