doc: write release notes for Go 1.28

This is the tracking issue for writing the Go 1.28 Release Notes. The version at tip can be viewed at https://tip.golang.org/doc/go1.28.

When we have a fairly complete release notes draft, enough for the needs of Go 1.28 RC 1, we should add okay-after-rc1 label here. The release-blocker label can be removed once everything else is done, including resolving all known items and those caught by `relnote todo`.

The draft notice stays until it's removed on the day of the release. At that time this issue is closed, and a similar issue is made for the next release. (The previous issue was #78779.)

Start with the Go 1.28 release notes draft at https://tip.golang.org/doc/go1.28 and review the tracking issue's requirements for RC 1 and the final release. Run or review `relnote todo` to identify known missing items. Done means the draft is sufficiently complete for RC 1, all known items are resolved, and the release notice can be removed when Go 1.28 ships.

Written by the indexing model from the issue text.