network_traffic: explicitly license under Elastic 1.0

[efd6]

What does this PR do?

Fixes license notice.

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

• [ ]

How to test this PR locally

Related issues

• Fixes [Network Packet Capture] Add license.txt #7149

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Build stats

• Start Time: 2023-07-26T22:14:50.135+0000

• Duration: 66 min 56 sec

Test stats 🧪

Test	Results
Failed	0
Passed	154
Skipped	0
Total	154

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (1/1)	💚
Files	100.0% (2/2)	💚
Classes	100.0% (2/2)	💚
Methods	98.276% (57/58)	👎 -1.724
Lines	88.356% (129/146)	👎 -11.644
Conditionals	100.0% (0/0)	💚

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Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[elasticmachine]

Package network_traffic - 1.19.3 containing this change is available at https://epr.elastic.co/search?package=network_traffic