fix(yaml) do not crash when the specified YAML array index does not exist

[dduportal]

Fix #439

This was a quick one that fixes a real bug (a case on limit).

Thanks to the amount of unit tests that @olblak did on the homemade YAML parser, it was easy to add a failing case, and then fix it.

Now, the following error is thrown when an out of bounds index is specified for YAML arrays:

ERROR: ✗ cannot find key "spec.containers[1].name" in the YAML file ".tmp/PodTemplates.yaml"

Test

To test this pull request, you can run the following commands:

$ make test-short # Fails without the fix on `pkg/plugins/yaml/main.go`
$ go build -o ./dist/updatecli && ./dist/updatecli diff --config ./.tmp/updatecli.yaml --values ~/workspace/jenkins-infra/kubernetes-management/updatecli/values.yaml

Additional Information

• Also removed the "non cleaned" yaml file that was still commited (caught by @lemeurherve in his PR ❤️ ).
• Took the opportunity to switch the Test_Replace() to the testify/assert instructions