Add labels to issue templates (#1301)

Signed-off-by: mueller-ma <mueller-ma@users.noreply.github.com>

.github/ISSUE_TEMPLATE/bug-report.md

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 name: Bug report
 about: 'Create a report to help us improve the openHAB client for Android'
+labels: bug
 
 ---
 

.github/ISSUE_TEMPLATE/feature_request.md

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 name: Feature request
 about: Suggest an idea for the openHAB client for Android
+labels: enhancement
 
 ---
 
-**Is your feature request related to a problem? Please describe.**
+### Is your feature request related to a problem? Please describe.
 A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
 
-**Describe the solution you'd like**
+### Describe the solution you'd like
 A clear and concise description of what you want to happen.
 
-**Describe alternatives you've considered**
+### Describe alternatives you've considered
 A clear and concise description of any alternative solutions or features you've considered.
 
-**Additional context**
+### Additional context
 Add any other context or screenshots about the feature request here.