network_traffic: add docs for configuration options

[efd6]

What does this PR do?

This adds configuration documentation for the network_traffic integration.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

Author's Checklist

• There is also a change in the flows manifest and hbs template removing the processes config options. This should have been done in network_traffic: expose configuration options to users #3157 but was missed. Formally this makes the change here a breaking change, though note that it could not have worked previously because the full set of monitored config options was not sent to packetbeat. Advice on how to proceed appreciated.

How to test this PR locally

Related issues

• Relates Network Packet Capture GA Blockers #1767

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• Start Time: 2022-05-23T14:19:44.324+0000

• Duration: 71 min 43 sec

Test stats 🧪

Test	Results
Failed	0
Passed	264
Skipped	0
Total	264

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[efd6]

The documentation on interface is intentionally weak here (see query here).

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