[chore][Feature Request Template] Comment out header descriptions (op…

…en-telemetry#9732)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
The descriptions for each header in the feature request template for
this repository are useful to the person filing a request, but serve no
purpose to the issue reader. These can be commented out to in the
displayed markdown to save the user from having to delete each one (or
if not deleted, save the reader from having to parse through extra
information).

.github/ISSUE_TEMPLATE/feature_request.md

@@ -15,15 +15,15 @@ not be prioritized.
 _Delete this paragraph before submitting._
 
 **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 [...]
+<!-- A clear and concise description of what the problem is. Ex. I'm always frustrated when [...] -->
 
 **Describe the solution you'd like**
-A clear and concise description of what you want to happen.
+<!-- A clear and concise description of what you want to happen. -->
 
 **Describe alternatives you've considered**
-A clear and concise description of any alternative solutions or features you've considered.
+<!-- A clear and concise description of any alternative solutions or features you've considered. -->
 
 **Additional context**
-Add any other context or screenshots about the feature request here.
+<!-- Add any other context or screenshots about the feature request here. -->
 
 _Please delete paragraphs that you did not use before submitting._