deployment: Adapt 'workerThreads' to be a string

There is a check in the main.go module which expects it to be a string so it can convert
it into an integer. Without this, we cannot actually provide the configuration without
hitting a conversion error. This should fix it.

deploy/chart/local-path-provisioner/templates/deployment.yaml

@@ -58,7 +58,7 @@ spec:
             - {{ .Values.configmap.name }}
           {{- if .Values.workerThreads }}
             - --worker-threads
-            - {{ .Values.workerThreads }}
+            - {{ .Values.workerThreads | toString }}
           {{- end }}
           {{- if .Values.provisioningRetryCount }}
             - --provisioning-retry-count