Configure ISSUE_TEMPLATE

Add a issue template type selector.

Live demo: https://github.com/smnandre/ux-issues/issues/new/choose

This is a start that allow to:
* differenciate bug & features
* add tags automatically
* expose the symfony support page

I'd like to release this first step asap.. and then iterate on the different forms.

Author: smnandre

.github/ISSUE_TEMPLATE/1-bug_report.md

@@ -0,0 +1,8 @@
+---
+name: '🐞 Bug Report'
+about: Report a bug in existing features
+title: ''
+labels: 'bug'
+assignees: ''
+
+---

.github/ISSUE_TEMPLATE/2-feature_request.md

@@ -0,0 +1,8 @@
+---
+name: '🚀 Feature Request'
+about: Suggest ideas for new features or enhancements
+title: ''
+labels: 'RFC'
+assignees: ''
+
+---

.github/ISSUE_TEMPLATE/3-documentation.md

@@ -0,0 +1,9 @@
+---
+name: '📖 Documentation'
+about: Help us improve the documentation!
+title: ''
+labels: 'docs'
+assignees: ''
+
+---
+

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,5 @@
+blank_issues_enabled: true
+contact_links:
+  - name: 🛟 Support / help
+    url: https://symfony.com/support
+    about: Ask your questions about Symfony UX