handle release/dist tags for published artifacts when there are multiple dev branches

[trentm]

A new 4.x major of elastic-apm-node is coming. We will have two active branches: 3.x for 3.x releases and main for 4.x releases. We need to make sure that published artifacts don't collide -- in particular the "latest" tag or marker for the various registries. The plan is detailed in comments below.

Original description:
We have added support for CI-based npm publish ... on new vX.Y.Z version tags. When we do a new major (4.x) and may then have new maintenance releases of the previous major (3.x), then we need to make sure that the npm publish becomes npm publish --tag <some-tag-name-other-than-"latest">. Otherwise a 3.x release will be incorrectly npm-dist-tagged with "latest".

[trentm]

npm dist-tag plan:

• we want latest on the current dev branch (currently "main"): use npm publish or npm publish --tag=latest
• let's use latest-<major>, e.g. "latest-3", for releases from a maintenance branch. When 4.x releases are GA (i.e. no longer prereleases) and 3.x is only for maintenance releases, let's use npm publish --tag=latest-3. We can't publish without a dist-tag, because npm publish doesn't support that, AFAIK.
• for pre-releases for a new major that is not yet GA, lets use prerelease. Note: We don't plan to publish any prereleases.

docker tag plan:
There is nothing we need to do here, because the current ./dev-scripts/push-docker.sh script (a) publishes docker.elastic.co/observability/apm-agent-nodejs:1.2.3 and (b) only tags and publishes docker.elastic.co/observability/apm-agent-nodejs:latest if the current release tag is the latest according to git tag --list --sort=version:refname "v*".

github releases tag plan:
By default gh release create ... will tag with "latest" by default. Their CLI docs say "automatic based on date and version", which is totally unclear to me. However, apparently gh release create --latest=false ... can be used to avoid that. So the plan is the "3.x" maintenance branch "release.yml" should update to use that --latest=false flag. We could add an explicit --latest flag on the "main" branch.

AWS Lambda Layers tag plan:
There is no tagging of "latest" here, that I know of, so there is nothing to do here.

These are all the published artifacts for a release. (I'm excluding the docs. That will be handled separately.)

[trentm]

This was all handled in #3573 which was pushed to the "dev/4.x" branch... as long as the newly documented steps in "CONTRIBUTING.md" for a release are followed.