added client generator inteface

[vardhaman-surana]

---

Description

• the functions to start services were tightly coupled with ClientGenerator. This PR modifies those function to accept clientGen as an argument.
• This PR adds a ClientGeneratorInterface so that ClientGenerator can be mocked if needed to write unit test cases for the function which requires ClientGenerator.

Which issue(s) this PR fixes:

Fixes # N/A

Testing

ran make check and make test-run locally.

Checklist:

• I ran tests as well as code linting locally to verify my changes.
• I have done manual verification of my changes, changes working as expected.
• I have added new tests to cover my changes.
• My changes follow contributing guidelines of Fission.
• I have signed all of my commits.

[codecov]

Codecov Report

Merging #2854 (7f8d41d) into main (c6329ee) will increase coverage by 0.03%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #2854      +/-   ##
==========================================
+ Coverage   20.91%   20.94%   +0.03%     
==========================================
  Files          68       68              
  Lines        7326     7313      -13     
==========================================
  Hits         1532     1532              
+ Misses       5682     5669      -13     
  Partials      112      112              

Flag	Coverage Δ
unittests	20.94% <0.00%> (+0.03%)	⬆️

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

Files	Coverage Δ
pkg/router/router.go	0.00% <0.00%> (ø)

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