[cisco_secure_email_gateway] Correct escaping to match both Unix and Windows-style paths

[chrisberkhout]

What does this PR do?

This fixes the change attempted in #7452. The problem was insufficient escaping.

Here's a summary of the various versions:

Original pattern raw:
^%{DATA}/%{WORD:cisco_secure_email_gateway.log.category.name}.@%{GREEDYDATA}.s$

Fixed pattern raw:
^%{DATA}/[\\/]%{WORD:cisco_secure_email_gateway.log.category.name}.@%{GREEDYDATA}.s$

Assumed fixed pattern as the broken string:
"^%{DATA}[\\/]%{WORD:cisco_secure_email_gateway.log.category.name}.@%{GREEDYDATA}.s$"

Assumed fixed pattern, raw from the broken string:
^%{DATA}[\/]%{WORD:cisco_secure_email_gateway.log.category.name}.@%{GREEDYDATA}.s$

Actually fixed pattern as the correct string:
"^%{DATA}[\\\\/]%{WORD:cisco_secure_email_gateway.log.category.name}.@%{GREEDYDATA}.s$"

Actually fixed pattern, raw from the correct string:
^%{DATA}[\\/]%{WORD:cisco_secure_email_gateway.log.category.name}.@%{GREEDYDATA}.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: 2023-08-29T11:58:30.828+0000

• Duration: 16 min 26 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)	👎 -16.667
Classes	83.333% (10/12)	👎 -16.667
Methods	89.286% (50/56)	👍 4.458
Lines	86.667% (598/690)	👎 -9.388
Conditionals	100.0% (0/0)	💚

[elasticmachine]

Package cisco_secure_email_gateway - 1.11.2 containing this change is available at https://epr.elastic.co/search?package=cisco_secure_email_gateway