[FEAT] Improve Configuration File: disable scan & per device binary

[lars18th]

Is your feature request related to a problem? Please describe.
This is partially related to #746 . After reading the example.collector.yaml I see two questions that cuold be improved:

1. How to disable the scanning process? If we use the devices: section to customize the configuration then the scanning process can be disabled. So in case of using a custom smartctl binary this proces meaningless and could be overridden. However, the custom config file doesn't have this option.
2. The smartctl binary override (metrics_smartctl_bin) is only global wide. And not per device. This could be a problem if we want to mix multiple binaries.

Describe the solution you'd like
Add these two changes to the configuration file:

devices:
#  # example to show how to override the smartctl command args (per device), see below for how to override these globally.
#  - device: /dev/sda
#    commands:
#      metrics_info_args: '--info --json -T permissive' # used to determine device unique ID & register device with Scrutiny
#      metrics_smart_args: '--xall --json -T permissive' # used to retrieve smart data for each device.
# NEW:
#      metrics_smartctl_bin: 'smartctl' # change to provide custom `smartctl` binary path, eg. `/usr/sbin/smartctl`

# example to show how to override the smartctl command args globally
#commands:
#  metrics_scan_args: '--scan --json' # used to detect devices
# NEW:
#  metrics_scan_args: '' # use '' or 'disabled' to not execute the scanning process

That's very simple: the metrics_smartctl_bin will have per device value. And if the metrics_scan_args is empty or disabled the process will not be executed.

Additional context
I hope you accept to implement this.