Add missing omitempty that breaks compatibility

Adding "omitempty" on the optional "description" field in WorkspacePipelineDeclaration, to be compatible with previous versions.

v1alpha1 is type aliased with v1beta1, but a new optional field is added.

Submitting without "omitempty" will result in an error from the admission webhook: "webhook.tekton.dev" denied the request: mutation failed: cannot decode incoming new object: json: unknown field: "description"

By adding "omitempty" tag, this field is not sent to the server when empty.

pkg/apis/pipeline/v1beta1/workspace_types.go

@@ -81,7 +81,7 @@ type WorkspacePipelineDeclaration struct {
 	// used in the Pipeline. It can be useful to include a bit of detail about which
 	// tasks are intended to have access to the data on the workspace.
 	// +optional
-	Description string `json:"description"`
+	Description string `json:"description,omitempty"`
 }
 
 // WorkspacePipelineTaskBinding describes how a workspace passed into the pipeline should be