Add direclty the file header of generated mocks

[ccojocar]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

Adds directly the file header of the generated mocks instead of doing post processing which cased duplicated header on macos.

Which issue(s) this PR fixes:

This allow to run the make verify command on macos during development. The current implementation generates a duplicated header which causes a dirty tree.

Does this PR have test?

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Add directly the file header when generating the mock types.

[codecov-commenter]

Codecov Report

Merging #1295 (991330e) into main (868709e) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1295   +/-   ##
=======================================
  Coverage   43.92%   43.92%           
=======================================
  Files          49       49           
  Lines        5514     5514           
=======================================
  Hits         2422     2422           
  Misses       2972     2972           
  Partials      120      120           

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ccojocar, JAORMX

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[ccojocar]

@JAORMX Please could you lgtm again this pull request? Thanks

[pjbgf]

/lgtm