metrics: update grafana template to add heartbeat latency overview

[nolouch]

What problem does this PR solve?

Issue Number: Ref #7897

What is changed and how does it work?

metrics: update grafana template to add heartbeat latency overview

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
  

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• JmPotato
• rleungx

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.32%. Comparing base (d7c7a41) to head (53ed412).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8209      +/-   ##
==========================================
+ Coverage   77.26%   77.32%   +0.06%     
==========================================
  Files         471      471              
  Lines       61425    61425              
==========================================
+ Hits        47459    47498      +39     
+ Misses      10398    10364      -34     
+ Partials     3568     3563       -5     

Flag	Coverage Δ
unittests	77.32% <ø> (+0.06%)	⬆️

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[nolouch]

/merge

[ti-chi-bot]

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 53ed412