[Feat] Dedicated "backup" role for "own machine" deployments

[pat-s]

Problem

It is currently not possible to run pgbackrest in combination with s3 storage endpoints without enabling a cloud provider and letting autobase do the machine provisioning.

Description

Add a dedicated "backup" role alongside a new option backup_provider which is called by the playbook tasks pgbackrest and executes/configures the respective backup provider in combination with either pgbackrest or wal_g.

I already have a working prototype of this an use and can create a PR, if wanted.

Importance

nice to have

Proposed implementation

No response

[vitabaks]

I believe it’s possible. We just need to move this condition from the playbook to the cloud resources tasks, ensuring that individual tasks related to configuring the S3 Bucket and auto_conf (pgabckrest and wal-g) are executed if the backup_provider variable is declared.

This way, we can skip creating a VM in the cloud while still automating backups setup.

@pat-s Feel free to prepare a PR