File-style Secret support in Kubernetes Provider

[RichardChen820]

Currently Kubernetes Provider does only support generating file-style ConfigMap. not support file-style Secret. This causes some inconvenience when someone is using file-style configMap, they may have to do some special for secrets.

Assume the target configuration should look like this:

{
   "database": {
       "connectionString": "xx"
   },
   "otherConfig": "fake-value",
   "otherConfig2": "fake-value2"
}

The database:connectionString comes from Secret, otherConfig* comes from configMap. Currently since k8s provider does not support file-style secret, it's not easy to tackle this situation.