Don't render checkboxes in issue template

.github/ISSUE_TEMPLATE/00-bug-issue.yml

@@ -1,16 +1,12 @@
 name: 🐛 Bug Report
 description: Use this template for reporting a bug
 body:
-  - type: checkboxes
+  - type: markdown
     attributes:
-      label: Is there an existing issue for this?
-      description: |
+      value: |
         Please search among past open/closed issues for a similar one beforehand:
           - https://github.com/Chocobozzz/PeerTube/issues?q=
           - https://framacolibri.org/c/peertube
-      options:
-        - label: I have searched existing issues
-          required: true
 
   - type: textarea
     attributes:

.github/ISSUE_TEMPLATE/10-installation-issue.yml

@@ -1,16 +1,12 @@
 name: 🚀 Installation/Upgrade Issue
 description: Use this template for build/installation/upgrade issues
 body:
-  - type: checkboxes
+  - type: markdown
     attributes:
-      label: Have you read the documentation?
-      description: |
+      value: |
         Please check the official documentation first
           - Classic installation: https://docs.joinpeertube.org/install-any-os
           - Docker installation: https://docs.joinpeertube.org/install-docker
-      options:
-        - label: I have read the documentation
-          required: true
 
   - type: checkboxes
     attributes:

.github/ISSUE_TEMPLATE/20-documentation-issue.yml

@@ -2,16 +2,12 @@ name: 📝 Documentation Issue
 description: Use this template for documentation-related issues
 labels: [ 'Component: Documentation :books:' ]
 body:
-  - type: checkboxes
+  - type: markdown
     attributes:
-      label: Is there an existing issue for this?
-      description: |
+      value: |
         Please search among past open/closed issues for a similar one beforehand:
           - https://github.com/Chocobozzz/PeerTube/issues?q=
           - https://framacolibri.org/c/peertube
-      options:
-        - label: I have searched existing issues
-          required: true
 
   - type: textarea
     attributes:

.github/ISSUE_TEMPLATE/30-feature-request.yml

@@ -2,16 +2,12 @@
 name: ✨ Feature Request
 description: Use this template to ask for new features and suggest new ideas 💡
 body:
-  - type: checkboxes
+  - type: markdown
     attributes:
-      label: Is there an existing issue for this?
-      description: |
+      value: |
         Please search among past open/closed issues for a similar one beforehand:
           - https://github.com/Chocobozzz/PeerTube/issues?q=
           - https://framacolibri.org/c/peertube
-      options:
-        - label: I have searched existing issues
-          required: true
 
   - type: textarea
     attributes: