chore(rubocop): move `LineLength` cop from `Metrics` to `Layout`

[dafyddj]

PR progress checklist (to be filled in by reviewers)

• [ ] Changes to documentation are appropriate (or tick if not required)
• [ ] 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
• [x] [chore] Changes to the build process or auxiliary tools and libraries such as documentation generation
• [ ] [ci] Changes to the continuous integration configuration
• [ ] [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

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

Does this PR introduce a BREAKING CHANGE?

No.

Related issues and/or pull requests

rubocop-hq/rubocop#7542

Describe the changes you're proposing

Upstream RuboCop have moved the LineLength cop from the Metrics department to the Layout department. Although the current setting still works, running RuboCop results in a warning, and we must assume that the Metrics/LineLength setting will be deprecated at some point.

Pillar / config required to test the proposed changes

Debug log showing how the proposed changes work

Get rid of this warning message: .rubocop.yml: Metrics/LineLength has the wrong namespace - should be Layout

Documentation checklist

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

Testing checklist

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

Additional context

[myii]

Thanks for resolving this, @dafyddj. The change has been propagated throughout the formulas using https://github.com/myii/ssf-formula/pull/129. Appreciate the review and merge, @baby-gnu.

[saltstack-formulas-travis]

:tada: This PR is included in version 4.0.4 :tada:

The release is available on GitHub release

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