update some Development Implements

[ayuki-joto]

🎩 What? Why?

• chore: fix typo decidem -> decidim on NEW_RELIC_APP_NAME chore: fix typo decidem -> decidim on NEW_RELIC_APP_NAME #248
• chore: enabled spot instance on staging environment chore: enabled spot instance on staging environment #251
• chore: add VPC & subnets Cloud Formation & INFRA.md chore: add VPC & subnets Cloud Formation & INFRA.md #249
• chore: add environment variable by SSM on ebextensions chore: add environment variable by SSM on ebextensions #245
• chore: Turn off New Relic except production chore: Turn off New Relic except production #258
• Fix locale file: decidim.errors.not_found.content_doesnt_exist Fix locale file: decidim.errors.not_found.content_doesnt_exist #262
• chore: change auto scale trigger to Average from Maximum chore: change auto scale trigger to Average from Maximum #265
• Fix ディベートを閉じた際のメールタイトルの翻訳がない #268; add locale for debate_closed Fix #268; add locale for debate_closed #269
• Fix fallbacks of i18n; use both :ja and :en Fix fallbacks of i18n; use both :ja and :en #270

📌 Related Issues

• Related to fix: add sidkiq&nginx docker image on eb #235 動作検証用アプリサーバがあると便利？ #110 DEPLOYMENT.mdにNEW_RELIC_LICENSE_KEYなどの環境変数の情報を追加する #193 本番環境のインスタンス数がおかしい #264
• Fixes development: NewRelicの警告が鬱陶しい #255 翻訳：住所 #260 ディベートを閉じた際のメールタイトルの翻訳がない #268

📋 Subtasks

• Add CHANGELOG upgrade notes, if required
• If there's a new public field, add it to GraphQL API
• Add documentation regarding the feature
• Add/modify seeds
• Add tests
• Another subtask