[syslog_router] Support Cisco IOS

[taylor-swanson]

Proposed commit message

Add support for Cisco IOS messages. Matches on the Cisco Emblem header in the log, and by default matches after Cisco ASA and FTD to avoid ambiguity.

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.
  - [ ] I have verified that any added dashboard complies with Kibana's Dashboard good practices

How to test this PR locally

1. Install assets for Cisco ASA, Cisco FTD, and Cisco IOS
2. Configure the Syslog Router integration (no changes necessary to routing configs).
3. Send Cisco ASA, FTD, and IOS logs to agent running integration
4. Verify that logs have landed in the correct data streams

I manually verified that logs were routed to the correct data streams.

Related issues

• Closes [Syslog_Router]: Support routing to Cisco IOS in the default template #15337

[elastic-vault-github-plugin-prod]

🚀 Benchmarks report

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[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: fc8aac5

cc @taylor-swanson

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube

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Pinging @elastic/integration-experience (Team:Integration-Experience)

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Package syslog_router - 0.3.0 containing this change is available at https://epr.elastic.co/package/syslog_router/0.3.0/