Link to OTel Go website_docs via submodule

[chalin]

This is a first illustration of #661 for open-telemetry/opentelemetry-go, which doesn't yet have a docs-update GitHub action. In fact, this relieves OTel Go maintainers from pushing doc update PRs to this repo, and so they won't require a docs-update GitHub action.

Aside from updated date/time stamps, there are no changes to the generated site files:

$ cd public && git diff -I '^<meta \w+="[^"]*(date|time)' -I '>Last modified' -- . ':(exclude)*.xml'
$

Preview: https://deploy-preview-690--opentelemetry.netlify.app/docs/go/

/cc @carlosalberto @shelbyspees

[chalin]

Note: once open-telemetry/opentelemetry-go#2189 is merged, the page GitHub links, like Edit this page, will point to the OTel Go repo.

(With the use of submodules, I could actually show you a preview of open-telemetry/opentelemetry-go#2189 by referring to the PR branch, but I won't set that up now to avoid confusion.)

[chalin]

Oops, I forgot to cc the OTel Go maintainers in the opening comment, so I'm doing it here.
/cc @Aneurysm9 @MrAlias

[chalin]

open-telemetry/opentelemetry-go#2189 has been reviewed and merged (thanks @Aneurysm9 @MrAlias!), so I refreshed the submodule in this PR.

You can now preview the Go page GH links: https://deploy-preview-690--opentelemetry.netlify.app/docs/go/

[chalin]

Thanks for the approval of this PR @MrAlias!