Add/log memory usage

[BraunRudolf]

Pull Request

Description

Solving: Issue: log memory usage #171

add memory logging in pv_stie_api.cache.remove_old_cache

• logging of memory after removing old cache entries

add requirement psutil

add tests/test_cache.py

• testing entry removal
• testing correct logging messages

new requirement: psutil

Fixes #171

How Has This Been Tested?

Unit-Test

Checklist:

• [x] My code follows OCF's coding style guidelines
• [x] I have performed a self-review of my own code
• [ ] I have made corresponding changes to the documentation
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have checked my code and corrected any misspellings

[sentry-io[bot]]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: pv_site_api/cache.py

Function	Unhandled Issue
remove_old_cache	RuntimeError: dictionary changed size during iteration /sites/pv_... Event Count: 1
remove_old_cache	RuntimeError: dictionary changed size during iteration /sites/{site_uuid}/pv_fo... Event Count: 1

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[peterdudfield]

Thank you @BraunRudolf