Translate using DeepL's API

[gottu91-code]

Tasks

• Complete the following TODO

Todo name: DeepLのAPIを使って翻訳する
file: src/routes/api/translate-with-deepl/[text=translation_text]/[target_locale_code=locale_code]/+server.ts
target function: GET関数

Writing the Issue

• Write each task for this issue using checkboxes
• Write all verbal instructions as tasks
• Add labels and assignees

Before Working on the Issue

• Assign yourself
• Share your screen on Discord
• Write which issue you are starting on Slack
• Git: Fetch the latest main
• Git: Create a branch with the name of the issue

Pre-PR Checks

• Insure that changes include only what is necessary for this PR
• Implement necessary Unit tests
• Implement necessary E2E tests
• Perform functionality checks