fix: skip empty k8s resources

[qa-ship-it]

What this PR does / why we need it:

While using the Gator CLI (v3.9.0) to test helm rendered k8s resources against our Gatekeeper constraints we ran into the following error: auditing objects: adding data of GVK "/, Kind=": admission.k8s.gatekeeper.sh: invalid request object: resource has no version
After investigation we found out that the error was due to a input file like the following one:

---
# Source: some/templates/file.yaml
name: object1
attrs:
  - attr1
  - attr2
---
# Source: some/templates/file.yaml
# only containing some comment
---
# Source: some/templates/file.yaml
name: object2
labels:
  - label1
  - label2

Apparently Gator CLI attempts to parse above snippet as 3 seperate YAML documents, looking for k8s resources inside them, which won't work as the second one containing only the comment cannot be parsed into a valid k8s resource at all.
This PR suggests skipping empty k8s resources.

[maxsmythe]

LGTM, thank you for the fix!

[codecov-commenter]

Codecov Report

Merging #2247 (1540232) into master (510da53) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2247      +/-   ##
==========================================
- Coverage   54.57%   54.55%   -0.03%     
==========================================
  Files         111      111              
  Lines        9554     9556       +2     
==========================================
- Hits         5214     5213       -1     
+ Misses       3946     3943       -3     
- Partials      394      400       +6     

Flag	Coverage Δ
unittests	54.55% <100.00%> (-0.03%)	⬇️

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

Impacted Files	Coverage Δ
pkg/gator/read_constraints.go	86.32% <100.00%> (+11.54%)	⬆️
...onstrainttemplate/constrainttemplate_controller.go	56.83% <0.00%> (-3.12%)	⬇️
pkg/readiness/object_tracker.go	82.91% <0.00%> (-1.07%)	⬇️

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[ritazh]

LGTM

Thanks for the PR! 🎉