harden service_facts states and add new output variable load_states

[jameslivulpi]

SUMMARY

#76629

• Better handling of the correct states across systemd
• Added a load_state field as this is easily accessible in the calls so shouldn't require much overhead. This allows user to see if unit is not-found, static, loaded, etc.
• Added integration tests including failed service test.

ISSUE TYPE

• Bugfix Pull Request

COMPONENT NAME

service_facts

[jameslivulpi]

I added some comments on the rationale behind some of changes in code, will remove those later and lint code further.

[jameslivulpi]

Reason I changed run_command to list style was to make linter happy :-)

[bcoca]

sorry for the delay on getting back, can you rebase the PR?

[opoplawski]

Nice to see --no-legend being added.

[bcoca]

note (not for immediate action): i've been thinking about this and more general PRs, adding a 'extended_info' for the plugin and then allow for each 'service system' to attach all 'extra' information seems a better approach than adding piece by piece the information to solve one problem at a time.

i.e service_facts: attach_extra_info=true would return ALL the fields that are not already part of the 'standard' return for a service under a extras/expanded: key.