Add tags

Add tags to allow more granular tasks filtering.
Add generator script for MD formatted tags found.
Add docs for tags how-to.

Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>

roles/kubernetes/secrets/tasks/main.yml

@@ -1,6 +1,8 @@
 ---
 - include: check-certs.yml
+  tags: [k8s-secrets, facts]
 - include: check-tokens.yml
+  tags: [k8s-secrets, facts]
 
 - name: Make sure the certificate directory exits
   file:
@@ -34,5 +36,6 @@
   notify: set secret_changed
 
 - include: gen_certs.yml
-
+  tags: k8s-secrets
 - include: gen_tokens.yml
+  tags: k8s-secrets