Adds a rake task to detect missing translations

[cypher]

Description

This adds a Rake task that compares the English translation keys for Avo with the Avo translations in the other locales, and reports any missing translations. If any are found, it exits with error code 1. It ignores any locales that don't have translations in the avo scope.

Run it with bundle exec rake avo:i18n:missing_translations

This could e.g. be run as part of a pre-release workflow to ensure that all locales have the required translation keys. This would prevent issues like #3400.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works

Screenshots & recording

Part of the output of this task if run against the current main branch:

Note that this shows the key from #3400 as missing in the de locale, amongst others.

Manual review steps

1. Run the rake task.
2. Add one of the missing translations.
3. Re-run the rake task, and see if the key is still reported as missing.

[codeclimate]

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[Paul-Bob]

Thank you for your contribution, @cypher!

We already have an i18n test at spec/system/i18n_spec.rb. The underlying issue was an outdated list of locales in config/i18n-tasks.yml. I've updated this list in PR #3402, so all locales should now be verified correctly.

Thanks once again, but I'll be closing this PR due to the reasons outlined above.

[cypher]

@Paul-Bob no worries, as long as it's fixed :)