Adds dns challenge issue template

Author: chaptergy

.github/ISSUE_TEMPLATE/dns_challenge_request.md

@@ -0,0 +1,18 @@
+---
+name: DNS challenge provider request
+about: Suggest a new provider to be available for a certificate DNS challenge
+title: ''
+labels: dns provider request
+assignees: ''
+
+---
+
+**What provider would you like to see added to NPM?**
+<!-- What is this provider called? -->
+
+
+**Have you checked if a certbot plugin exists?**
+<!-- 
+Currently NPM only supports DNS challenge providers for which a certbot plugin exists. 
+You can visit pypi.org, and search for a package with the name `certbot-dns-<privider>`.
+-->