CV2-5558: Downgrade based on last_seen, not created_at; add better logging

[computermacgyver]

Description

Better log when and why a relationship is downgraded from a confirmed match to a suggestion. When downgrading for an "old" match, use last_seen, not created_at

References: CV2-5558

How has this been tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can verify the changes. Please describe whether or not you implemented automated tests.

Things to pay attention to during code review

Please describe parts of the change that require extra attention during code review, for example:

• File FFFF, line LL: This refactoring does this and this. Is it consistent with how it’s implemented elsewhere?
• Etc.

Checklist

• I have performed a self-review of my own code
• I have added unit and feature tests, if the PR implements a new feature or otherwise would benefit from additional testing
• I have added regression tests, if the PR fixes a bug
• I have added logging, exception reporting, and custom tracing with any additional information required for debugging
• I considered secure coding practices when writing this code. Any security concerns are noted above.
• I have commented my code in hard-to-understand areas, if any
• I have made needed changes to the README
• My changes generate no new warnings
• If I added a third party module, I included a rationale for doing so and followed our current guidelines

[caiosba]

@computermacgyver if you need help to fix this test, please let us know: Bot::AlegreTest#test_should_set_similarity_relationship_based_on_date_threshold [/app/test/models/bot/alegre_test.rb:204].