enable issue template chooser with templates for bug report, feature

request and documentation

.github/ISSUE_TEMPLATE/bug_report.yml

+name: Bug Report
+description: Create a report to help us reproduce and fix the bug
+labels: ["bug"]
+
+body:
+- type: markdown
+  attributes:
+    value: >
+      #### Thank you for contributing! Before reporting a bug, please have a look at the [FAQ](https://github.com/opencv/opencv/wiki/FAQ), make sure the issue has no duplicate and hasn't been already addressed by searching through [the existing and past issues](https://github.com/opencv/opencv/issues?page=1&q=is%3Aissue+sort%3Acreated-desc).
+
+- type: textarea
+  attributes:
+    label: System Information
+    description: |
+      Please provide the following system information to help us diagnose the bug. For example:
+
+      // example for c++ user
+      OpenCV version: 4.6.0
+      Operating System / Platform: Ubuntu 20.04
+      Compiler & compiler version: GCC 9.3.0
+
+      // example for python user
+      OpenCV python version: 4.6.0.66
+      Operating System / Platform: Ubuntu 20.04
+      Python version: 3.9.6
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Detailed description
+    description: |
+      Please provide a clear and concise description of what the bug is and paste the error log below. It helps improving readability if the error log is wrapped in ```` ```triple quotes blocks``` ````.
+    placeholder: |
+      A clear and concise description of what the bug is.
+
+      ```
+      # error log
+      ```
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Steps to reproduce
+    description: |
+      Please provide a minimal example to help us reproduce the bug. Code should be wrapped with ```` ```triple quotes blocks``` ```` to improve readability. If the code is too long, please attach as a file or create and link a public gist: https://gist.github.com.
+
+      Related data files (images, onnx, etc) should be attached below as well. If the data files are too big, feel free to upload them to a online drive, share them and put the link below.
+    placeholder: |
+      ```cpp (replace cpp with python if python code)
+      # sample code to reproduce the bug
+      ```
+
+      Test data: [image](https://link/to/the/image), [model.onnx](htts://link/to/the/onnx/model)
+  validations:
+    required: true
+- type: checkboxes
+  attributes:
+    label: Issue submission checklist
+    options:
+      - label: I report the issue, it's not a question
+        required: true
+      - label: I checked the problem with documentation, FAQ, open issues, forum.opencv.org, Stack Overflow, etc and have not found any solution
+      - label: I updated to the latest OpenCV version and the issue is still there
+      - label: There is reproducer code and related data files (videos, images, onnx, etc)

.github/ISSUE_TEMPLATE/config.yml

+blank_issues_enabled: true
+contact_links:
+  - name: Questions
+    url: https://forum.opencv.org/
+    about: Ask questions and discuss with OpenCV community members

.github/ISSUE_TEMPLATE/documentation.yml

+name: Documentation
+description: Report an issue related to https://docs.opencv.org/
+labels: ["category: documentation"]
+
+body:
+- type: markdown
+  attributes:
+    value: >
+      #### Thank you for contributing! Before submitting a doc issue, please make sure it has no duplicate by searching through [the existing and past issues](https://github.com/opencv/opencv/issues?page=1&q=is%3Aissue+sort%3Acreated-desc)
+
+- type: textarea
+  attributes:
+    label: Descripe the doc issue
+    description: >
+      Please provide a clear and concise description of what content in https://docs.opencv.org/ is an issue. Note that there are multiple active branches, such as 3.4, 4.x and 5.x, so please specify the branch with the problem.
+    placeholder: |
+      A clear and concise description of what content in https://docs.opencv.org/ is an issue.
+
+      Link to the doc: https://docs.opencv.org/4.x/d3/d63/classcv_1_1Mat.html
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Fix suggestion
+    description: >
+      Tell us how we could improve the documentation in this regard.

.github/ISSUE_TEMPLATE/feature_request.yml

+name: Feature request
+description: Submit a request for a new OpenCV feature
+labels: ["feature"]
+
+body:
+- type: markdown
+  attributes:
+    value: >
+      #### Thank you for contributing! Before submitting a feature request, please make sure the request has no duplicate by searching through [the existing and past issues](https://github.com/opencv/opencv/issues?page=1&q=is%3Aissue+sort%3Acreated-desc)
+
+- type: textarea
+  attributes:
+    label: Descripe the feature and motivation
+    description: |
+      Please provide a clear and concise proposal of the feature and outline the motivation.
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Additional context
+    description: |
+      Add any other context, such as pseudo code, links, diagram, screenshots, to help the community better understand the feature request.