fix: consider terminated a non existing DataFlow

[ndr-brt]

What this PR changes/adds

Add null checks on the dataPlaneId in the DataPlaneSignalingFlowController

Why it does that

Avoid exceptions: terminating a DataFlow that does not exist will return success, because it can implicitly be considered terminated

Further notes

• added the check also on the suspend method, but it work differently, it will return failure if dataPlaneId is null, because a non existing data flow cannot be suspended and that needs to be notified.

Linked Issue(s)

Closes #4418

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.97%. Comparing base (7f20ba5) to head (b6ea76d).
Report is 389 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4420      +/-   ##
==========================================
+ Coverage   71.74%   74.97%   +3.22%     
==========================================
  Files         919     1075     +156     
  Lines       18457    21473    +3016     
  Branches     1037     1172     +135     
==========================================
+ Hits        13242    16099    +2857     
- Misses       4756     4854      +98     
- Partials      459      520      +61     

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