docs: add network metrics attributes from OBI

[mvanhorn]

Ports 6 new network flow attributes to Beyla docs.

Why this matters

OBI PR #8914 added network.type, network.protocol.name, and geoip fields (src/dst country, src/dst ASN) to the metrics reference. Beyla's docs were missing them.

Changes

• docs/sources/network/_index.md: Added 6 rows to the network attributes table after dst.zone

Testing

Docs-only change. Verified table formatting matches existing rows.

Fixes #2422

This contribution was developed with AI assistance (Claude Code).

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[cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 47.88%. Comparing base (2f9aa74) to head (3bfd36f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2636      +/-   ##
==========================================
+ Coverage   43.30%   47.88%   +4.58%     
==========================================
  Files          57       57              
  Lines        5025     4212     -813     
==========================================
- Hits         2176     2017     -159     
+ Misses       2682     2055     -627     
+ Partials      167      140      -27     

Flag	Coverage Δ
beyla-integration-test	?
integration-test	?
integration-test-arm	?
integration-test-vm-x86_64-5.15.152	?
integration-test-vm-x86_64-6.10.6	?
k8s-integration-test	?
oats-test	?
unittests	47.88% <ø> (ø)

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