Update issue templates

.github/ISSUE_TEMPLATE/--work-item--dev-only-.md

+---
+name: "\U0001F528Work Item (DEV ONLY)"
+about: Work item issue for tracking progress. Dev team only.
+title: ''
+labels: Work Item
+assignees: ''
+
+---
+
+## 🔨Work Item
+
+**IMPORTANT:**
+* This template is only for dev team to track project progress. For feature request or bug report, please use the corresponding issue templates.
+* DO NOT create a new work item if the purpose is to fix an existing issue or feature request. We will directly use the issue in the project tracker.
+
+Project tracker: https://github.com/orgs/dmlc/projects/2
+
+## Description
+
+<!-- short description of the work item -->
+
+## Depending work items or issues
+
+<!-- what must be done before this -->

.github/ISSUE_TEMPLATE/bug-report.md

----
-name: "\U0001F41B Bug Report"
-about: Submit a bug report to help us improve DGL
-
----
-
-## 🐛 Bug
-
-<!-- A clear and concise description of what the bug is. -->
-
-## To Reproduce
-
-Steps to reproduce the behavior:
-
-1.
-1.
-1.
-
-<!-- If you have a code sample, error messages, stack traces, please provide it here as well -->
-
-## Expected behavior
-
-<!-- A clear and concise description of what you expected to happen. -->
-
-## Environment
-
- - DGL Version (e.g., 1.0):
- - Backend Library & Version (e.g., PyTorch 0.4.1, MXNet/Gluon 1.3):
- - OS (e.g., Linux):
- - How you installed DGL (`conda`, `pip`, source):
- - Build command you used (if compiling from source):
- - Python version:
- - CUDA/cuDNN version (if applicable):
- - GPU models and configuration (e.g. V100):
- - Any other relevant information:
-
-## Additional context
-
-<!-- Add any other context about the problem here. -->
+---
+name: "\U0001F41B Bug Report"
+about: Submit a bug report to help us improve DGL
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+## 🐛 Bug
+
+<!-- A clear and concise description of what the bug is. -->
+
+## To Reproduce
+
+Steps to reproduce the behavior:
+
+1.
+1.
+1.
+
+<!-- If you have a code sample, error messages, stack traces, please provide it here as well -->
+
+## Expected behavior
+
+<!-- A clear and concise description of what you expected to happen. -->
+
+## Environment
+
+ - DGL Version (e.g., 1.0):
+ - Backend Library & Version (e.g., PyTorch 0.4.1, MXNet/Gluon 1.3):
+ - OS (e.g., Linux):
+ - How you installed DGL (`conda`, `pip`, source):
+ - Build command you used (if compiling from source):
+ - Python version:
+ - CUDA/cuDNN version (if applicable):
+ - GPU models and configuration (e.g. V100):
+ - Any other relevant information:
+
+## Additional context
+
+<!-- Add any other context about the problem here. -->

.github/ISSUE_TEMPLATE/documentation.md

----
-name: "\U0001F4DA Documentation"
-about: Report an issue related to docs.dgl.ai
-
----
-
-## 📚 Documentation
-
-<!-- Please specify whether it's tutorial part or API reference part-->
-<!-- Describe the issue.-->
+---
+name: "\U0001F4DA Documentation"
+about: Report an issue related to docs.dgl.ai
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+## 📚 Documentation
+
+<!-- Please specify whether it's tutorial part or API reference part-->
+<!-- Describe the issue.-->

.github/ISSUE_TEMPLATE/feature-request.md

----
-name: "\U0001F680Feature Request"
-about: Submit a proposal/request for a new DGL feature
-
----
-
-## 🚀 Feature
-<!-- A brief description of the feature proposal -->
-
-## Motivation
-
-<!-- Please outline the motivation for the proposal. Is your feature request
-related to a problem? e.g., I'm always frustrated when [...]. If this is
-related to another GitHub issue, please link here too -->
-
-## Alternatives
-
-<!-- A clear and concise description of any alternative solutions or features you've considered, if any. -->
-
-## Pitch
-
-<!-- A clear and concise description of what you want to happen. -->
-
-## Additional context
-
-<!-- Add any other context or screenshots about the feature request here. -->
+---
+name: "\U0001F680Feature Request"
+about: Submit a proposal/request for a new DGL feature
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+## 🚀 Feature
+<!-- A brief description of the feature proposal -->
+
+## Motivation
+
+<!-- Please outline the motivation for the proposal. Is your feature request
+related to a problem? e.g., I'm always frustrated when [...]. If this is
+related to another GitHub issue, please link here too -->
+
+## Alternatives
+
+<!-- A clear and concise description of any alternative solutions or features you've considered, if any. -->
+
+## Pitch
+
+<!-- A clear and concise description of what you want to happen. -->
+
+## Additional context
+
+<!-- Add any other context or screenshots about the feature request here. -->

.github/ISSUE_TEMPLATE/questions-help-support.md

----
-name: "❓Questions/Help/Support"
-about: Do you need support? We have resources.
-
----
-
-## ❓ Questions and Help
-
-Before proceeding, please note that we recommend
-using our discussion forum (https://discuss.dgl.ai) for
-general questions. As a result, this issue will
-likely be CLOSED shortly.
+---
+name: "❓Questions/Help/Support"
+about: Do you need support? We have resources.
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+## ❓ Questions and Help
+
+Before proceeding, please note that we recommend
+using our discussion forum (https://discuss.dgl.ai) for
+general questions. As a result, this issue will
+likely be CLOSED shortly.

.github/ISSUE_TEMPLATE/work-item.md

+---
+name: Work Item
+about: Describe this issue template's purpose here.
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+