[8.0](backport #29331) x-pack/filebeat/module/sophos/xg: fix kv field separation and add support for timestamped log line

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This is an automatic backport of pull request #29331 done by Mergify.

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• Start Time: 2022-01-04T07:25:14.549+0000

• Duration: 102 min 49 sec

• Commit: 12cd829

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Test	Results
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Skipped	1275
Total	10872

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