WIP: Internationalization and localization

[matthiasschaub]

Description

This PR uses FastAPI-I18N to configure gettextfor each request based on the accept-language header.

It also uses babel to work with message catalogs.

Currently, indicator metadata and result string templates are translated.

Corresponding issue

Closes #

New or changed dependencies

• babel
• fastapi-i18n

Checklist

• I have ensured my branch is mergeable with main (e.g. through git rebase main if necessary)
• My code follows the style guide and was checked with pre-commit before committing
• I have commented my code
• I have added sufficient unit and integration tests
• I have added new Hurl regression tests and checked all existing tests
• I have updated the CHANGELOG.md

Todos

• Add unit tests for successful translation of result string templates.
• Add integration tests (API) which tests the fallback to Englishh if no accept-language header is set, accept-header is set but does not exist and fastapi-i18n is not configured properly.
• Update environment var mock to not use absolute path.
• Translate figure