[Wf-Diagnostics] remove heartbeat rootcause for other irrelevant timeouts

[sankari165]

What changed?
Update the way wf-diagnostics provides heart beating as a solution for activity timeouts

Why?
Rootcause mentioning heartbeat is not relevant for schedule to start timeouts or for non heartbeat timeouts with heart beating enabled

How did you test it?
unit tests

Potential risks

Release notes

Documentation Changes

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 72.99%. Comparing base (630013c) to head (ab2aaab).
Report is 1 commits behind head on master.

Files	Patch %	Lines
service/worker/diagnostics/invariants/timeout.go	93.33%	1 Missing ⚠️

Additional details and impacted files

Files	Coverage Δ
service/worker/diagnostics/invariants/timeout.go	86.20% <93.33%> (+3.59%)	⬆️

... and 6 files with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 630013c...ab2aaab. Read the comment docs.