x-pack/filebeat/module/sophos/xg: fix kv field separation and add support for timestamped log line

[efd6]

What does this PR do?

This fixes KV field separation and adds support for log lines that have syslog-style timestamps and hostname headers.

Why is it important?

The current situation is breaking some users.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Author's Checklist

• Check relevant section of https://docs.sophos.com/nsg/sophos-firewall/18.5/PDF/SF%20syslog%20guide%2018.5.pdf for origin of last test case.

How to test this PR locally

Python integration tests for x-pack filebeat,

Related issues

• Fixes [Filebeat] Dissect Parsing Error with Sophos Module #24237

Use cases

N/A

Screenshots

N/A

Logs

N/A

[elasticmachine]

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

[efd6]

First commit is the interesting one, second is entirely mechanical.

[elasticmachine]

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Build stats

• Start Time: 2022-01-04T04:51:57.514+0000

• Duration: 107 min 22 sec

• Commit: 3721b6b

Test stats 🧪

Test	Results
Failed	0
Passed	9638
Skipped	1275
Total	10913

💚 Flaky test report

Tests succeeded.

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[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b sophos/fw upstream/sophos/fw
git merge upstream/master
git push upstream sophos/fw

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b sophos/fw upstream/sophos/fw
git merge upstream/master
git push upstream sophos/fw

[adriansr]

LGTM