docs: add PR templates for closed issues and community contributions

.github/PR_TEMPLATE/closed_issue.md

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+<!--- Provide a general summary of your changes in the Title above -->
+
+## Description
+
+<!--- Describe your changes in detail -->
+
+## Related Issue
+
+<!--- This project only accepts pull requests related to open issues -->
+<!--- If suggesting a new feature or change, please discuss it in an issue first -->
+<!--- If fixing a bug, there should be an issue describing it with steps to reproduce -->
+<!--- Please link to the issue here: -->
+
+## Motivation and Context
+
+<!--- Why is this change required? What problem does it solve? -->
+<!--- If it fixes an open issue, please link to the issue here. -->
+
+## How Has This Been Tested?
+
+<!--- Please describe in detail how you tested your changes. -->
+<!--- Include details of your testing environment, and the tests you ran to -->
+<!--- see how your change affects other areas of the code, etc. -->
+
+## Screenshots (if appropriate):

.github/PR_TEMPLATE/community_contrib.md

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+- **Please check if the PR fulfills these requirements**
+
+* [ ] The commit message follows our guidelines
+* [ ] Tests for the changes have been added (for bug fixes / features)
+* [ ] Docs have been added / updated (for bug fixes / features)
+
+- **What kind of change does this PR introduce?** (Bug fix, feature, docs update, ...)
+
+- **What is the current behavior?** (You can also link to an open issue here)
+
+- **What is the new behavior (if this is a feature change)?**
+
+- **Does this PR Close an issue?** (If applicable, please add the number of the issue here with keyword Closes)
+
+- **Does this PR introduce a breaking change?** (What changes might users need to make in their application due to this PR?)
+
+- **Other information**: