Adapt Elasticsearch spec to stability changes

[gregkalapos]

Follow up from https://github.com/open-telemetry/semantic-conventions/pull/974#discussion_r1584002801.

Changes

• Align Elasticsearch span names with the format defined in the general db spec. MongoDB is comparable and it already follows this format. The idea is to not only have the operation (endpoint id) in the span name, but also the target.
• Adding db.collection.name to the Elasticsearch spec, which is used in the span name as well.
• Changed the last fallback in the span name from http.request.method to db.system. The thinking behind this is that db.system is usually the last fallback for other DBs. This was also the outcome in https://github.com/open-telemetry/semantic-conventions/issues/704. In practice this fallback is used extremely rarely since endpoint id is usually available.

Questions

• [ ] db.elasticsearch.cluster.name could be replaced with db.namespace. Do we want to do that?
• [ ] I think we could consider making this stable at this point. Any thoughts on this? I'd prefer to try to make this stable.

Merge requirement checklist

• [x] CONTRIBUTING.md guidelines followed.
• [x] Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• [ ] schema-next.yaml updated with changes to existing conventions.