automate create serviceaccout if there is no serviceAccount specified in sparkapp yaml

[xrmzju]

roles need by spark lancher is is fixed(https://github.com/GoogleCloudPlatform/spark-on-k8s-operator/blob/master/manifest/spark-rbac.yaml), we need create the sa manually now, which is not so convenient.

[xrmzju]

@liyinan926 ,what do you think about this idea?

[liyinan926]

This could be a feature for operator deployments that limits the operation of the operator to a single namespace. The feature could be enabled/disabled through a command-line flag. If enabled, the operator automatically creates the RBAC role and service account for that namespace, and automatically patches SparkApplication instances submitted to the namespace to use the service account. This helps save quite a lot of work from users.

[liyinan926]

@KoopaKing is this relevant?