Update roadmap
Update roadmap

- Add milestones for the end of the year. 0.9 is a bit optimistic
- Add link from milestone version to the corresponding release
- Moved completed items to the correct milestones.

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MOS_MIGRATED_REVID=118761783

davidzchen/bazel-website,davidzchen/bazel-website,davidzchen/bazel-website,bazelbuild/bazel-website,davidzchen/bazel-website,bazelbuild/bazel-website,bazelbuild/bazel-website