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/dnsmasq/meta/main.yml

@@ -3,3 +3,4 @@ dependencies:
   - role: download
     file: "{{ downloads.dnsmasq }}"
     when: not skip_dnsmasq|default(false) and download_localhost|default(false)
+    tags: [download, dnsmasq]

roles/dnsmasq/tasks/main.yml

@@ -1,5 +1,7 @@
 ---
 - include: dnsmasq.yml
   when: "{{ not skip_dnsmasq_k8s|bool }}"
+  tags: dnsmasq
 
 - include: resolvconf.yml
+  tags: resolvconf