Add 3 dashes (---) at start of each manifest to avoid concatenation errors

[jlamillan]

Not all the manifests in the manifest directory start with three dashes ("---").

As I understand it, YAML uses three dashes ("---") to signal both the start of a new document and to separate document content.

Not following guidelines and being inconsistent can create difficult to find errors for tools that combine and apply multiple manifest files together (e.g. Rancher user-addons).