ci: allow conditional secrets for docker login

[skl]

Turns out if: secrets is not valid GitHub Actions workflow syntax on forks, so to make this docker login step optional we need to first use another step to actually check the secret.

Then use output from above step as the condition. This should be more compatible.

To take advantage of this during the release process, the secret needs to be passed in from the parent workflow using secrets: inherit and registered as an optional secret in the workflow_call definition.

[mmat11]

🤞🏻

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 43.91%. Comparing base (0e24aab) to head (2cb4809).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1441      +/-   ##
==========================================
- Coverage   44.89%   43.91%   -0.98%     
==========================================
  Files         312      313       +1     
  Lines       28901    34213    +5312     
==========================================
+ Hits        12974    15025    +2051     
- Misses      15136    18210    +3074     
- Partials      791      978     +187     

Flag	Coverage Δ
integration-test	21.55% <ø> (?)
integration-test-arm	0.00% <ø> (?)
integration-test-vm-x86_64-5.15.152	0.00% <ø> (?)
integration-test-vm-x86_64-6.10.6	0.00% <ø> (?)
k8s-integration-test	2.29% <ø> (?)
oats-test	0.00% <ø> (?)
unittests	44.91% <ø> (+0.02%)	⬆️

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