refactor: use pathlib in sbom_manager/__init__.py

[terriko]

We're partway through a migration from the older os.path method of handling filesystem paths to the newer Pathlib style, and have a number of files that need updating. I'm filing a separate bug for each so folk doing hacktoberfest can grab one and go really quickly and hopefully so people won't wind up doing too much overlapping work and people can indicate they're working on one by commenting on it.

Basically, the task is to search through the file for the string os.path and replace whatever's there with the equivalent Pathlib construction.

• Here's an example of the type of changes needed to switch to pathlib.
• Pathlib docs

Here's a quick grep on the file to show you what probably needs to be changed:

cve_bin_tool/sbom_manager/__init__.py:            if os.path.exists(self.filename):

Don't forget to remove any imports that are no longer needed when you're done! (you can use flake8 to check for those).

[gulyapulya]

Hi, my previous issue got taken, so I decided to work on this one instead. Thanks.