Replace direct usage of getent_passwd with ansible_facts.getent_passwd
in both client_setup.yml and server_setup.yml.

Ansible 2.24+ will remove the INJECT_FACTS_AS_VARS feature, requiring
explicit use of ansible_facts dictionary instead of top-level fact
variables.

Fixes deprecation warning:
  INJECT_FACTS_AS_VARS default to 'True' is deprecated, top-level facts
  will not be auto injected after the change.

Adds option to choose a non-default borg backup user on the server.

This brings support for multiple backups pointing to the same borg
server, different repositories, from the same client. We support this by
parsing the SSH authorized key file first and appending allowed
repositories to allow independent definitions of the borg targets.

So that the decryption_keys do not clash we include the repository name
as well as the host in the key. This will lead to new keys being created
for existing hosts in the new format.

    Old Format: {{ combine({inventory_hostname: borg_keys.stdout}) }}
    New Format: {{ combine({(inventory_hostname ~ '_' ~ borg_repo_name): borg_keys.stdout}) }}

If upgrading from an older version that used just the hostname as the
key, your existing `decryption_keys.yml` can be manually removed once
the new format is also added.

Fix linting errors that came up with the new rules

Main changes:
* Enforce YAML document start headers
* Enforce spacing with commas, colons and hyphens
* Enforce indentation
* Enforce use of quotes only then required
* Enforce use of single quotes over double quotes
* Enforce use of true/false over yes/no and derivatives
* [..] Other minor rules that were already followed

Signed-off-by: Colin Wilk <colin.wilk@tum.de>

Signed-off-by: Colin Wilk <colin.wilk@tum.de>