Add labels in github template metadata

Ref: https://help.github.com/articles/creating-issue-templates-for-your-repository/

.github/ISSUE_TEMPLATE/bug-report.md

@@ -1,6 +1,7 @@
 ---
 name: Bug Report
 about: Report a bug encountered while operating Kubernetes
+labels: kind/bug
 
 ---
 
@@ -22,6 +23,3 @@ about: Report a bug encountered while operating Kubernetes
 - Kernel (e.g. `uname -a`):
 - Install tools:
 - Others:
-
-<!-- DO NOT EDIT BELOW THIS LINE -->
-/kind bug

.github/ISSUE_TEMPLATE/enhancement.md

@@ -1,6 +1,7 @@
 ---
 name: Enhancement Request
 about: Suggest an enhancement to the Kubernetes project
+labels: kind/feature
 
 ---
 <!-- Please only use this template for submitting enhancement requests -->
@@ -8,6 +9,3 @@ about: Suggest an enhancement to the Kubernetes project
 **What would you like to be added**:
 
 **Why is this needed**:
-
-<!-- DO NOT EDIT BELOW THIS LINE -->
-/kind feature

.github/ISSUE_TEMPLATE/failing-test.md

@@ -1,6 +1,7 @@
 ---
 name: Failing Test
 about: Report test failures in Kubernetes CI jobs
+labels: kind/failing-test
 
 ---
 
@@ -17,6 +18,3 @@ about: Report test failures in Kubernetes CI jobs
 **Reason for failure**:
 
 **Anything else we need to know**:
-
-<!-- DO NOT EDIT BELOW THIS LINE -->
-/kind failing-test

.github/ISSUE_TEMPLATE/support.md

@@ -1,6 +1,7 @@
 ---
 name: Support Request
 about: Support request or question relating to Kubernetes
+labels: triage/support
 
 ---
 
@@ -15,8 +16,3 @@ You can also post your question on the [Kubernetes Slack](http://slack.k8s.io/)
 
 If the matter is security related, please disclose it privately via https://kubernetes.io/security/.
 -->
-
-<!-- DO NOT EDIT BELOW THIS LINE -->
-
-/triage support
-