Support generating multiple YAML documents from one template

[ryannedolan]

A template like SqlJob.yaml.template can include multiple documents, separated by ---. This is could be useful if one Resource needs to be implemented with multiple Kubernetes objects. For example, a SqlJob could be implemented as a FlinkDeployment and a ConfigMap.

However, the operator currently treats each Resource as a single document, and makes one call to the Kubernetes API for each. Instead, the operator should:

1. Generate yaml by applying templates, as it does now.
2. Split the output yaml into separate documents.
3. Apply each document individually.

It is probably insufficient to just String.split on ---, as this sequence may appear in the template in an escaped string. Instead, the YAML parser should be used to parse the YAML into a list of documents.