[BUG] Gem doesn't work on servers which don't have git installed

[willlahr]

Describe the bug
This gem does not work when git is not installed - this can be a problem in production servers, even if git based deployment is used. It is because it does this in the gemspec:

 spec.files         = `git ls-files`.split($/)

I fixed it like this:

      spec.files         = `du -a`.split("\n").map{|line| line.split("\t")[1].sub('./','')} - ["spec", "samples", ".github/ISSUE_TEMPLATE", ".github", "lib/marketingcloudsdk", "lib", "."]

Note: Because the developers need to copy and paste the code snippet, including a code snippet as a media file (e.g. gif) is not sufficient.

Environment

• SDK Version [e.g. 1.2.0]
• Ruby version

The bug has the severity

• Critical: The defect affects critical functionality or critical data. It does not have a workaround.
• Major: The defect affects major functionality or major data. It has a workaround but is not obvious and is difficult.
• Minor: The defect affects minor functionality or non-critical data. It has an easy workaround.
• Trivial: The defect does not affect functionality or data. It does not even need a workaround. It does not impact productivity or efficiency. It is merely an inconvenience.

Additional context
Add any other context about the problem here.