Fix notification operator

[anandtiwary]

Description

Please include a summary of the change, motivation and context.
Only shows success message when at least one value has been emitted on source observable.

Testing

Please describe the tests that you ran to verify your changes. Please summarize what did you test and what needs to be tested e.g. deployed and tested helm chart locally.

Checklist:

• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• Any dependent changes have been merged and published in downstream modules

Documentation

Make sure that you have documented corresponding changes in this repository or hypertrace docs repo if required.

[codecov]

Codecov Report

Merging #673 (20d168e) into main (0234ae5) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #673   +/-   ##
=======================================
  Coverage   85.22%   85.22%           
=======================================
  Files         780      780           
  Lines       16054    16056    +2     
  Branches     2070     2071    +1     
=======================================
+ Hits        13682    13684    +2     
  Misses       2337     2337           
  Partials       35       35           

Impacted Files	Coverage Δ
...omponents/src/notification/notification.service.ts	96.29% <100.00%> (+0.29%)	⬆️

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[github-actions]

Unit Test Results

    4 files  ±0  244 suites  ±0   15m 8s ⏱️ -50s
878 tests ±0  878 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
882 runs  ±0  882 ✔️ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 3822823. ± Comparison against base commit 0234ae5.