Automate doc publishing to opentelemetry.io

[tigrannajaryan]

We now have a manually triggered github action doc-update which publishes the documentation from this repo to opentelemetry.io website repo (creates a PR there).

It would be nice to automate triggering of doc-update action as part of release process.

[tigrannajaryan]

FYI, @open-telemetry/collector-approvers

[cole-easton]

I would like to take this issue.