Fix docstring indent issue in feature files

[ernilambar]

Before:

    When I run `curl -sS localhost:8181`
    Then STDOUT should contain:
    """
    Just another WordPress site
    """

After:

    When I run `curl -sS localhost:8181`
    Then STDOUT should contain:
      """
      Just another WordPress site
      """

In our feature tests, we generally use indented docstring block. Majority of tests use this convention but there are some files which does not abide this.

Since there is no rules for this in gherkin-lint, I have developed custom rule for gherkin-lint. https://github.com/ernilambar/gherkin-lint-rules/blob/main/custom-rules/docstring-indent.js
Currently I am running this locally to detect issue and working on preparing PR for WPCLI repos. We can also integrate this rule in the central repo if deemed feasible.

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