x/website: add opensearch.xml

[xfmoulet]

What did you do?

using Firefox, select the "add godoc" as a search engine

What did you expect to see?

golang search engine added to Firefox

What did you see instead?

https://golang.org/opensearch.xml not found

copy/pasting this url in the adrowser gives an error page:

lstat $GOROOT/opensearch.xml: no such file or directory

[seankhliao]

Is it useful for golang.org to do this or is this better suited for pkg.go.dev (which includes the docs for stdlib)?

[seankhliao]

I just saw there's an opensearch file https://go.googlesource.com/website/+/refs/heads/master/content/static/opensearch.xml and it's linked via <link> tags but not served

[gopherbot]

Change https://golang.org/cl/290210 mentions this issue: godoc: expose opensearch

[gopherbot]

Change https://golang.org/cl/290230 mentions this issue: cmd/golangorg: register handler for opensearch.xml

[rsc]

Search box removed (#44357).