docs(github): Adjust issue templates to issue types

The "bug" and "enhancement" labels have been replaces by issues types of
the same names, and "new feature" was combined into "enhancement".

Signed-off-by: Sebastian Schuberth <sebastian@doubleopen.org>

Author: sschuberth

.github/ISSUE_TEMPLATE/bug.md

@@ -2,7 +2,8 @@
 name: Bug Report 🐞
 about: I want to report a bug that I am facing.
 title: ''
-labels: ['bug', 'to triage']
+type: 'Bug'
+labels: ['to triage']
 
 ---
 ### Describe the bug

.github/ISSUE_TEMPLATE/enhancement.md

@@ -1,11 +1,12 @@
 ---
 name: Enhancement Proposal ⚡
-about: I want to propose to enhance existing functionality.
+about: I want to propose some new functionality.
 title: ''
-labels: ['enhancement', 'to triage']
+type: 'Enhancement'
+labels: ['to triage']
 
 ---
-### What is the existing functionality and how should it be enhanced?
+### What is the functionality you want to propose?
 
 A clear and concise description of what you propose to change and why it is an enhancement.