doc/initial, doc/next: add draft notice to introduction
Go release notes always start out as a draft with a clear notice.
That notice is removed when the final release (go1.N.0) is made.
For example, the last time was in CL 562255.
Add this to the Go 1.23 draft and to the future fragment template.
Also switch to the main pkg.go.dev instance and use a relative issue
link in 3-tools.md while here.
For #64169.
For #65614.
Change-Id: I16bc0fa8a3a43ee7a9edd7fa253999041f1892e2
Reviewed-on: https://go-review.googlesource.com/c/go/+/587415 Reviewed-by: Jonathan Amsterdam <jba@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Bypass: Dmitri Shuralyov <dmitshur@golang.org>
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