Update virtual node defaults and change feature gate to beta

[ogxd]

Component(s)

connector/servicegraph

Context

Started with this discussion: grafana/tempo#3480 (reply in thread)
@joe-elliott

The servicegraph connector has a feature for creating virtual nodes. There are currently three issues:

• Some default values are now obsolete given semver (1.24).
  • net.peer.name (replaced by server.address on client spans and client.address on server spans)
  • net.sock.peer.name (removed)
  • net.sock.peer.addr (replaced by network.peer.address)
  • http.url (replaced by url.full)
  • http.target (split to url.path and url.query)
• The feature is behind an "alpha" feature gate, which prevents it from being used (eg using otelcol helm chart). Plus there is no mention of it being disabled by default in the documentation.
• Documentation is a little ambiguous

Proposition

• Change default values to peer.service, db.name and db.system (in this order). These are compliant with conventions, and the same as the tempo service graph uses.
• Switch the feature from "alpha" to "beta". Virtual nodes are working well on the tempo side, and feature could be disabled anyway by using an empty list if needed.
• Reword documentation for improved clarity

See PR: #31735

[github-actions]

Pinging code owners:

• connector/servicegraph: @jpkrohling @mapno

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[ogxd]

Hello @Frapschen, the PR has been reviewed, but it is waiting for approval from another maintainer which seems like he isn't receiving notifications or is busy (he is active on other issues). Would it be possible to get a approval/final review (if necessary) on this PR?

Thanks a lot 😄