Fix: create whole config path if it doesnt exist yet

[gauron99]

If the func config path doesnt exist at all yet, create it here, where strictly necessary.
WriteFile will create the auth.json file if necessary, but not the whole path.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 67.06%. Comparing base (8dce9bc) to head (2e2da73).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/docker/creds/credentials.go	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2490      +/-   ##
==========================================
+ Coverage   61.54%   67.06%   +5.52%     
==========================================
  Files         129      129              
  Lines       15340    11934    -3406     
==========================================
- Hits         9441     8004    -1437     
+ Misses       4972     2966    -2006     
- Partials      927      964      +37     

Flag	Coverage Δ
e2e-test	36.60% <0.00%> (-0.01%)	⬇️
e2e-test-oncluster	33.34% <0.00%> (-0.07%)	⬇️
e2e-test-oncluster-runtime	29.52% <0.00%> (?)
e2e-test-runtime-go	26.61% <0.00%> (?)
e2e-test-runtime-node	26.00% <0.00%> (?)
e2e-test-runtime-python	26.00% <0.00%> (?)
e2e-test-runtime-quarkus	26.09% <0.00%> (?)
e2e-test-runtime-rust	25.14% <0.00%> (?)
e2e-test-runtime-springboot	25.15% <0.00%> (?)
e2e-test-runtime-typescript	26.08% <0.00%> (?)
integration-tests	53.11% <0.00%> (+2.36%)	⬆️
unit-tests	51.29% <33.33%> (?)
unit-tests-macos-latest	?
unit-tests-ubuntu-latest	?
unit-tests-windows-latest	?

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[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gauron99, lkingland

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