sophos: fix handling of date parsing

[efd6]

What does this PR do?

Ensure fields that have been defined as date are parseable as date. Also add timezone configuration and progressively determine timezone from logs, config, locale.

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 [sophos][xg] Failed to parse field [sophos.xg.eventtime] exceptions #6546

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• Start Time: 2023-06-23T01:08:04.940+0000

• Duration: 19 min 21 sec

Test stats 🧪

Test	Results
Failed	0
Passed	31
Skipped	0
Total	31

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (2/2)	💚
Files	100.0% (13/13)	💚
Classes	100.0% (13/13)	💚
Methods	98.901% (90/91)	👍 0.037
Lines	93.776% (1808/1928)	👍 3.07
Conditionals	100.0% (0/0)	💚

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

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Package sophos - 2.11.0 containing this change is available at https://epr.elastic.co/search?package=sophos

[elasticmachine]

Package sophos - 2.11.0 containing this change is available at https://epr.elastic.co/search?package=sophos