[Ingest Manager] Windows agent doesn't uninstall with a lowercase c: drive in the path

[michalpristas]

What does this PR do?

This PR fixes uninstall check case sensitivity.
The problem was with windows that paths does not need to match case to work. New Func was added which either check strings for equality(darwin,linux) or checks them in case insensitive way (windows)

Why is it important?

Fixes #22268

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

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Pinging @elastic/agent (Team:Agent)

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Pinging @elastic/ingest-management (Team:Ingest Management)

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Build stats

• Build Cause: Pull request #23998 updated

• Start Time: 2021-02-11T13:36:58.412+0000

• Duration: 28 min 45 sec

• Commit: 9e87734

Test stats 🧪

Test	Results
Failed	0
Passed	5902
Skipped	16
Total	5918

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Test stats 🧪

Test	Results
Failed	0
Passed	5902
Skipped	16
Total	5918