Remove YamlFileResource#yamlObject

[ljacqu]

With the recent refactoring to export everything via SnakeYAML nodes, the field yamlObject in YamlFileResource has become obsolete as the SnakeYAML instance is only used once. I didn't want to clean it up immediately because it also involves removing various other methods, which we'll take care of in ConfigMe 2.0.

In the class YamlFileResource:

• Replace the only usage of getYamlObject with createNewYaml
• Remove method onWriteComplete -> probably has no point for anyone anymore?
• Remove the field yamlObject
• Rename createNewYaml to createYamlInstance or similar? (Maybe createSnakeYamlInstance is more descriptive?)

[aadya28]

Hi @ljacqu I have raised the PR with required refactoring changes, please review 😊