fixes #437: adding further locales to the image

[daudo]

🗣 Description

This patch enables WeeWX Docker containers to properly support international skins and extensions that rely on system locales for date/time formatting and translations. Currently, many skins and extensions (ie. the Belchertown skin) fail to display localized content because the required locales aren't available in the base image.

The change is minimal, and will probably useful for for international WeeWX users without any negative impact on existing deployments.

💭 Motivation and context

Give more flexibility for international users, fixes #437

🧪 Testing

I tested the changes by running locale -a in a running container. And also, the Belchertown skin worked flawlessly after adding the locales. And apart from that, those changes are trivial.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All relevant repo and/or project documentation has been updated
  to reflect the changes in this PR.

✅ Pre-merge checklist

• Revert dependencies to default branches.
• Finalize version.

✅ Post-merge checklist

• Add a tag or create a release.