Update issue templates and add pull_request template (#9345)

Author: iamrajiv

.github/ISSUE_TEMPLATE/bug.md

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+---
+name: 🐛 Bug Report
+labels: "bug"
+---
+
+<!--
+Note: If the problem you are reporting is about a specific library function, then the typeshed tracker is better suited
+for this report: https://github.com/python/typeshed/issues
+-->
+
+## 🐛 Bug Report
+
+(A clear and concise description of what the bug is.)
+
+## To Reproduce
+
+(Write your steps here:)
+
+1. Step 1...
+1. Step 2...
+1. Step 3...
+
+## Expected Behavior
+
+<!--
+  How did you expect your project to behave?
+  It’s fine if you’re not sure your understanding is correct.
+  Write down what you thought would happen. If you just expected no errors, you can delete this section.
+-->
+
+(Write what you thought would happen.)
+
+## Actual Behavior
+
+<!--
+  Did something go wrong?
+  Is something broken, or not behaving as you expected?
+-->
+
+(Write what happened.)
+
+## Your Environment
+
+<!-- Include as many relevant details about the environment you experienced the bug in -->
+
+- Mypy version used:
+- Mypy command-line flags:
+- Mypy configuration options from `mypy.ini` (and other config files):
+- Python version used:
+- Operating system and version:
+
+<!--
+You can freely edit this text, please remove all the lines
+you believe are unnecessary.
+-->

.github/ISSUE_TEMPLATE/documentation.md

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+---
+name: 📚 Documentation
+labels: "documentation"
+---
+
+## 📚 Documentation
+
+(A clear and concise description of the issue.)

.github/ISSUE_TEMPLATE/feature.md

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+---
+name: 🚀 Feature
+labels: "feature"
+---
+
+## 🚀 Feature
+
+(A clear and concise description of your feature proposal.)
+
+## Pitch
+
+(Please explain why this feature should be implemented and how it would be used. Add examples, if applicable.)

.github/ISSUE_TEMPLATE/question.md

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+---
+name: ❓ Questions and Help
+labels: "question"
+---
+
+## ❓ Questions and Help
+
+### Please note that this issue tracker is not a help form and this issue will be closed.
+
+Please contact us instead.
+
+- [Website](http://www.mypy-lang.org/)
+- [Gitter](https://gitter.im/python/typing)

.github/PULL_REQUEST_TEMPLATE.md

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+### Have you read the [Contributing Guidelines](https://github.com/python/mypy/blob/master/CONTRIBUTING.md)?
+
+(Once you have, delete this section. If you leave it in, your PR may be closed without action.)
+
+### Description
+
+<!--
+If this pull request closes or fixes an issue, write Closes #NNN" or "Fixes #NNN" in that exact
+format.
+-->
+
+(Explain how this PR changes mypy.)
+
+## Test Plan
+
+<!--
+If this is a documentation change, rebuild the docs (link to instructions) and review the changed pages for markup errors.
+If this is a code change, include new tests (link to the testing docs). Be sure to run the tests locally and fix any errors before submitting the PR (more instructions).
+If this change cannot be tested by the CI, please explain how to verify it manually.
+-->
+
+(Write your test plan here. If you changed any code, please provide us with clear instructions on how you verified your changes work.)