fix: updated gitignore paths to use forward slashes on Windows

[chrisbutulis]

Closes #10449

Change Description

Background

This fix ensures that automatic .gitignore entries are generated with backslashes on linux-based systems as well as on Windows-based systems.

Bug Fix

1. Problem - Currently the gitignore entries for directories generated using lakectl clone generate with backslashes on Windows, causing the .gitignore to malfunction and not actually ignore the directories.
2. Root cause - The function createEntriesForIgnore in git.go doesn't universalize file paths; it uses the convention of the user's operating system
3. Solution - I fixed the bug by wrapping the filepath.join() call in a filepath.ToSlash() call in createEntriesForIgnore, which changes directory backslashes forward slashes.

Testing Details

I added a testing file in the pkg/git subdirectory called git_internal_test.go, as the function createEntriesForIgnore is internal to the package "git". The test verifies that a temporary test directory is correctly named with a forward slash. The test passes locally on Windows.

Breaking Change?

Not that I am aware of.

Additional info

N/A

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