Enable configurations by default

[tacerus]

PR progress checklist (to be filled in by reviewers)

• [x] Changes to documentation are appropriate (or tick if not required)
• [x] Changes to tests are appropriate (or tick if not required)
• [ ] Reviews completed

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What type of PR is this?

Primary type

• [ ] [build] Changes related to the build system
• [ ] [chore] Changes to the build process or auxiliary tools and libraries such as documentation generation
• [ ] [ci] Changes to the continuous integration configuration
• [x] [feat] A new feature
• [ ] [fix] A bug fix
• [ ] [perf] A code change that improves performance
• [ ] [refactor] A code change that neither fixes a bug nor adds a feature
• [ ] [revert] A change used to revert a previous commit
• [ ] [style] Changes that do not affect the meaning of the code (white-space, formatting, missing semi-colons, etc.)

Secondary type

• [x] [docs] Documentation changes
• [ ] [test] Adding missing or correcting existing tests

Does this PR introduce a BREAKING CHANGE?

No - whilst the default behavior technically changes, practically the default behavior before this change would print an error message, hence nobody could have been using it so far.

Related issues and/or pull requests

Describe the changes you're proposing

On distributions without separate available/enabled directories it feels unnecessary having to declared enabled: true in every configuration block. I propose "enabling" configurations by default unless specified otherwise, instead of printing an error about enabled missing from the dict.

Pillar / config required to test the proposed changes

nginx:
  servers:
    managed:
      general.conf:
        available_dir: /etc/nginx/conf.d
        config:
        - server_names_hash_bucket_size: 128

Debug log showing how the proposed changes work

Documentation checklist

• [ ] Updated the README (e.g. Available states).
• [x] Updated pillar.example.

Testing checklist

• [ ] Included in Kitchen (i.e. under state_top).
• [ ] Covered by new/existing tests (e.g. InSpec, Serverspec, etc.).
• [ ] Updated the relevant test pillar.

Additional context

n/a