Automatically resolve the system hostname when running forget

[PHLAK]

Is your feature request related to a problem? Please describe.

I'm attempting to set up autorestic on multiple systems sharing one common (B2) backend. When running autorestic forget I'd like the system's hostname to be automatically resolved and passed to the --host option so that only snapshots for the current host will be forgot/pruned.

From the Removing Backup Snapshots documentation.

you can restrict the policy to only process snapshots which have a particular hostname with the --host parameter, or tags with the --tag option.

Describe the solution you'd like

Allow host: true (or host: auto) to be passed under the forget configuration. When set to true (or auto) it would automatically resolve the current system's hostname and pass that value as the --host option value.

Currently works

global:
  forget:
    host: my-hostname # Passes '--host my-hostname'

Desired solution

global:
  forget:
    host: true # Resolves the current host name and passes it as '--host <current_hostname>'