cloudflare_logpush: fix handling of timestamps for all available formats

[efd6]

What does this PR do?

See title.

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

• For Cloudflare Logpush integration does not support the correct available timestamp formats to match the output format options from the source #7762

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• Start Time: 2023-09-12T01:26:40.291+0000

• Duration: 25 min 6 sec

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Name	Metrics % (covered/total)	Diff
Packages	100.0% (15/15)	💚
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Classes	100.0% (15/15)	💚
Methods	100.0% (178/178)	💚
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Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[ShourieG]

LGTM, only one minor suggestion, can we give some comments explaining the conversion logic used, I know it's simple to understand for many, but would be a nice QoL feature for the average reader. An updated description in the PR also works.

[efd6]

I'll expand on it in the commit message.

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Package cloudflare_logpush - 1.8.1 containing this change is available at https://epr.elastic.co/search?package=cloudflare_logpush