🔧 use Github discussions for questions

.github/ISSUE_TEMPLATE/config.yml

+blank_issues_enabled: false
+contact_links:
+  - name: Ask a question
+    url: https://github.com/nlohmann/json/discussions
+    about: Ask questions and discuss with other community members

.github/ISSUE_TEMPLATE/question.md

----
-name: Question
-about: Ask a question regarding the library.
-title: ''
-labels: 'kind: question'
-assignees: ''
-
----
-
-<!-- Provide a concise summary of the issue in the title above. -->
-
-#### What do you want to achieve?
-
-<!-- Please describe the feature as detailed as possible. -->
-
-#### What have you tried?
-
-<!-- There are thousands of issues to search: https://github.com/nlohmann/json/issues?q=is%3Aissue+ -->
-<!-- There is a full documentation of the API: https://nlohmann.github.io/json/ -->
-<!-- There is a detailed README file: https://github.com/nlohmann/json/blob/develop/README.md -->
-
-#### Can you provide a small code example?
-
-<!-- Please understand that we cannot analyze and debug large code bases. -->
-
-#### Which compiler and operating system are you using?
-
-<!-- Include as many relevant details about the environment you experienced the bug in. -->
-<!-- Make sure you use a supported compiler, see https://github.com/nlohmann/json#supported-compilers. -->
-
-- Compiler: ___
-- Operating system: ___
-
-#### Which version of the library did you use?
-
-<!-- Please add an `x` to the respective line. -->
-
-- [ ] latest release version 3.7.3
-- [ ] other release - please state the version: ___
-- [ ] the `develop` branch