[cisco_secure_email_gateway] Match both Unix and Windows-style paths

[chrisberkhout]

What does this PR do?

Adjust a Grok pattern applied to log.file.path so that it matches Windows-style paths like V:\\DATA\\mail_logs.@20230817T054656.s as well as Unix-style paths like /data/mail_logs.@20230817T054656.s.

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.

How to test this PR locally

Doesn't break existing tests:

cd packages/cisco_secure_email_gateway elastic-package test 

Related issues

• Relates https://github.com/elastic/sdh-beats/issues/3729

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

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Build stats

• Start Time: 2023-08-17T16:50:10.373+0000

• Duration: 16 min 25 sec

Test stats 🧪

Test	Results
Failed	0
Passed	23
Skipped	0
Total	23

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (1/1)	💚
Files	83.333% (10/12)	👎 -11.111
Classes	83.333% (10/12)	👎 -11.111
Methods	89.286% (50/56)	👍 3.333
Lines	86.667% (598/690)	👍 0.643
Conditionals	100.0% (0/0)	💚

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Package cisco_secure_email_gateway - 1.11.1 containing this change is available at https://epr.elastic.co/search?package=cisco_secure_email_gateway