[github] add new templates

.github/ISSUE_TEMPLATE/bug_template.md

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+---
+name: 🐛 Bug report
+about: Create a report to help us improve
+title: "[BUG]"
+labels: 'bug, untriaged'
+assignees: ''
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**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.
+
+**Plugins**
+Please list all plugins currently enabled.
+
+**Screenshots**
+If applicable, add screenshots to help explain your problem.
+
+**Host/Environment (please complete the following information):**
+ - OS: [e.g. iOS]
+ - Version [e.g. 22]
+
+**Additional context**
+Add any other context about the problem here.

.github/ISSUE_TEMPLATE/config.yml

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+# disable blank issue creation
+blank_issues_enabled: false

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: 🎆 Feature request
+about: Suggest an idea for this project
+title: ''
+labels: 'enhancement, untriaged'
+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/pull_request_template.md

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+### Description
+[Describe what this change achieves]
+
+### Issues Resolved
+[List any issues this PR will resolve]
+
+### Check List
+- [ ] New functionality includes testing.
+  - [ ] All tests pass
+- [ ] New functionality has been documented.
+  - [ ] New functionality has javadoc added
+- [ ] Commits are signed per the DCO using --signoff
+- [ ] Commit changes are listed out in CHANGELOG.md file (See: [Changelog](../blob/main/CONTRIBUTING.md#changelog))
+
+By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
+For more information on following Developer Certificate of Origin and signing off your commits, please check [here](https://github.com/opensearch-project/OpenSearch/blob/main/CONTRIBUTING.md#developer-certificate-of-origin).