[docs] Added Issue Template, PR Template, updated CONTRIBUTING

[skip ci]

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Open a bug report
+title: "[bug] "
+labels: bug
+assignees: ''
+
+---
+
+**Describe the bug**
+A clear and concise description of the bug or unexpected behavior.
+
+**Steps To Reproduce**
+Steps to reproduce the behavior:
+1. Go to '...'
+2. Click on '....'
+3. Scroll down to '....'
+4. See error
+
+**Expected behavior**
+A clear and concise description of what you expected to happen.
+
+**Screenshots**
+If applicable, add screenshots to help explain your problem.
+
+**System Informatioon:**
+ - OS: [e.g. Ubuntu 24.04 LTS]
+ - Python Version: [e.g. Python 3.11.2]
+ - Django Version: [e.g. Django 4.2.5]
+ - Browser and Browser Version (if applicable): [e.g. Chromium v126.0.6478.126]

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Suggest an idea for this project
+title: "[feature] "
+labels: enhancement
+assignees: ''
+
+---
+
+**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**
+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.
+
+**Additional context**
+Add any other context or screenshots about the feature request here.

.github/ISSUE_TEMPLATE/question.md

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+---
+name: Question
+about: Please use the Discussion Forum to ask questions
+title: "[question] "
+labels: question
+assignees: ''
+
+---
+
+Please use the [Discussion Forum](https://github.com/orgs/openwisp/discussions) to ask questions.
+
+We will take care of moving the discussion to a more relevant repository if needed.

.github/pull_request_template.md

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+## Checklist
+
+- [ ] I have read the [OpenWISP Contributing Guidelines](http://openwisp.io/docs/developer/contributing.html).
+- [ ] I have manually tested the changes proposed in this pull request.
+- [ ] I have written new test cases for new code and/or updated existing tests for changes to existing code.
+- [ ] I have updated the documentation.
+
+## Reference to Existing Issue
+
+Closes #<issue-number>.
+
+Please [open a new issue](https://github.com/openwisp/openwisp-notifications/issues/new/choose) if there isn't an existing issue yet.
+
+## Description of Changes
+
+Please describe these changes.
+
+## Screenshot
+
+Please include any relevant screenshots.

openwisp_notifications/CONTRIBUTING.rst

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+Please refer to the `OpenWISP Contributing Guidelines <http://openwisp.io/docs/developer/contributing.html>`_.