[i18n] Support automatic banner management across localizations

[chalin]

• Fixes [i18n] Support non-English banners with English fallback #4486
• Fixes Figur out how to do "time-boxed" entries to the banner #4380
• Adds documentation on Announcements (the feature being proposed here to handle banners in a locale-friendly way). For details, see the added doc section.
• Converts the two existing banners to announcement pages, and copyedits the eBPF one
• Adds a ja banner for the OTel Community Day
• Adds a zh banner for the OTel Community Day
• Enables banners for ja and zh
• Changes the build scripts to exclude expired as well as future pages
• ~Implements English-fallback pages for ja--> will do this separately, see [i18n & ja] Improved fallback config and normalize en doc links #4627
• Adds an announcement archetype

Preview:

• https://deploy-preview-4625--opentelemetry.netlify.app/docs/contributing/#announcement-management
• https://deploy-preview-4625--opentelemetry.netlify.app
• https://deploy-preview-4625--opentelemetry.netlify.app/ja
• https://deploy-preview-4625--opentelemetry.netlify.app/zh

Screenshot

[chalin]

There's an issue which running scripts/i18n-check.sh -u in a GH action because apparently it doesn't have access to all the branches, or the expected branch, etc. I don't want to hold up this PR. I'll debug that separately.

@open-telemetry/docs-zh-approvers and @ymotongpoo: I'll assume that you are ok with the translations here for the OTel Community day. If not we can address the required changes in a followup PR.

[chalin]

All green, merging.

[ymotongpoo]

@chalin thanks! I checked Japanese translation for OTel community day banner and it looks perfect!

[chalin]

@ymotongpoo - thank you for confirming ✨