Use start_date instead of execution_date for ongoing duration metrics

[Kyle-Neale]

What does this PR do?

This PR uses the start_date instead of execution_date for ongoing duration metrics

Motivation

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.07%. Comparing base (826f684) to head (2bd371e).
Report is 15 commits behind head on master.

Additional details and impacted files

Flag	Coverage Δ
activemq	?
airflow	93.03% <100.00%> (+0.39%)	⬆️
cassandra	?
hive	?
hivemq	?
ignite	?
jboss_wildfly	?
kafka	?
presto	?
solr	?

Flags with carried forward coverage won't be shown. Click here to find out more.

[iliakur]

Just suggestions about the tests, implementation lgtm!

[iliakur]

not a blocker, but I think we can get rid of an if-clause in the test_config_collect_ongoing_duration implementation.