Migrate Apache Weex to alibaba/weex

## Background

Apache IPMC starts a lazy consensus vote (2021/05/09) for the [_Retirement of Weex_](https://lists.apache.org/x/thread.html/reb2523a568b5ce5cfc1b8017c20106221f0ab689ebcf3cb42feb8a54%40%3Cgeneral.incubator.apache.org%3E). The vote considered to be passed, and the Apache Weex project will retire to the [_attic_](https://attic.apache.org/) recently.

However, "[_retire_](https://incubator.apache.org/guides/retirement.html)" doesn't mean deprecated, Weex will continue to develop under [alibaba/weex](https://github.com/alibaba/weex).
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## Brief Timeline

- [2016-06-30]: Weex project open-sourced in GitHub [alibaba/weex](https://github.com/alibaba/weex).
- [2016-12-15]: Weex core team announced to donate Weex to [ASF](https://www.apache.org/) (Apache Software Foundation).
- [2017 ~ 2020]: Weex was incubating under ASF (Codebase: [apache/incubator-weex](https://github.com/apache/incubator-weex)), migrate the community and workflow to [_the apache way_](https://apache.org/theapacheway/).
- [2021-05-09]: Apache IPMC starts a vote for the retirement of Weex.
- [2021-05]: Weex team migrate codebase and workflow back to [alibaba/weex](https://github.com/alibaba/weex).

## Codebase Migration

Weex related repositories in [github.com/apache](https://github.com/apache) will turn to be [archived](https://docs.github.com/en/github/creating-cloning-and-archiving-repositories/archiving-a-github-repository), and migrate to other places.
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- [apache/incubator-weex](https://github.com/apache/incubator-weex): Major source code of Weex. Migrate to [alibaba/weex](https://github.com/alibaba/weex).
- [apache/incubator-weex-site](https://github.com/apache/incubator-weex-site): The official website of Weex. Migrate to [weexteam/website](https://github.com/weexteam/website).
- [apache/incubator-weex-cli](https://github.com/apache/incubator-weex-cli): Weex toolkit. Migrate to [weexteam/weex-toolkit](https://github.com/weexteam/weex-toolkit).
- [apache/incubator-weex-loader](https://github.com/apache/incubator-weex-loader): Webpack loader of Weex. Migrate to [weexteam/weex-loader](https://github.com/weexteam/weex-loader).
- [apache/incubator-weex-ui](https://github.com/apache/incubator-weex-ui): UI Components of Weex. Migrate to [weexteam/weex-ui](https://github.com/weexteam/weex-ui).
- [apache/incubator-weex-playground](https://github.com/apache/incubator-weex-playground): The playground App of Weex. Merge into [alibaba/weex](https://github.com/alibaba/weex).
- [apache/incubator-weex-android-compatible](https://github.com/apache/incubator-weex-android-compatible): Legacy android utils tool. Already archived.

## Other Actions

- Update README.md of apache/incubator-weex, and mark it to be archived.
- Add announcement on weex.apache.org, and move the website back to weex.io.
- Clean up outdated declaration files and re-configure CI on alibaba/weex.
- Migrate internal workflow to GitHub, such as feature discussion, issues, pull request, testing, roadmap, release note, etc.
- Publish a version for the latest code after migration.

Start by reviewing README.md in apache/incubator-weex and the listed destination repositories. Check the migration status of the site, CLI, loader, UI, and playground repositories, then review CI and workflow configuration in alibaba/weex. Done means the repositories and workflows are migrated or archived as listed, announcements are updated, and a post-migration release is published.

Written by the indexing model from the issue text.