Add new unreliable_los option

[aida-shumburo]

SUMMARY

Set interface configuration option for when to generate a 'loss of service' (LOS) alarm

GitHub Issues

"N/A"

ISSUE TYPE

• Feature Pull Request

COMPONENT NAME

sonic_interfaces

OUTPUT

Ansible Report:

add_unreliable_los.pdf

Raw Regression Test Output:

unreliable_los.zip

Checklist:

• I have performed a self-review of my own code to ensure there are no formatting, linting, or security issues
• I have verified that new and existing unit tests pass locally with my changes
• I have not allowed coverage numbers to degenerate
• I have maintained at least 90% code coverage
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have maintained backward compatibility or have provided any relevant "breaking_changes" descriptions in a "fragment" file in the "changelogs/fragments" directory of this repository.
• I have provided a summary for this PR in valid "fragment" file format in the "changelogs/fragments" directory of this repository branch. Reference : Ansible Change Log Document

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Please also list any relevant details for your test configuration

• I ran different ansible playbooks to test that the new ' unreliable_los' option value is being merged, replaced, deleted, and overriden the correct way
• Ran a regression test (attached above)

[kerry-meyer]

Thank you for providing this new functionality.

I am posting a few minor comments to address before merging of this PR.

[kerry-meyer]

Almost all of the pending "Issues" are "Resolved" by your most recent set of changes.

I have one remaining "Issue" related to setting up the required conditions for integration test_06.

Everything else looks good.

[kerry-meyer]

Thanks for making the final requested change.

All proposed code changes, added test cases, and test results look good.

Approved.