Report total physical system memory on Linux

[nr-ahemsath]

Description

Resolves #36.

Total system memory will now be reported by .NET core agents running on Linux systems. The agent reads /proc/meminfo and pulls out the MemTotal value.

Regarding testing: I considered adding a unit test for this, but the only real logic is the regex parsing of the MemTotal: 12345 kB line, and so a unit test using mock/fake /proc/meminfo data would just be testing that the regex works or doesn't. I can still add a unit test like this if desired; some refactoring would be required to make the method in question testable. We don't have any existing integration tests for this feature of the agent, and an integration test seems too heavyweight for this.

I did test this change manually on Ubuntu 20.04 and verified that the total physical memory was being sent in the utilization payload.

Author Checklist

• Unit tests, Integration tests, and Unbounded tests completed - see above statement
• Performance testing completed with satisfactory results (if required) - N/A
• Agent Changelog or Lambda Agent changelog updated

Reviewer Checklist

• Perform code review
• Pull request was adequately tested (new/existing tests, performance tests)
• Review Changelog

[tehbio]

Looks good! Don't forget to update the changelog.

[jaffinito]

Great comment!