[KYUUBI #1846] Add improvement issue template

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### _Why are the changes needed?_
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Please clarify why the changes are needed. For instance,
  1. If you add a feature, you can talk about the use case of it.
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As disused in https://github.com/apache/incubator-kyuubi/discussions/1824.

Below is a preview of the new issue template.

<img width="1022" alt="截屏2022-01-28 23 06 12" src="https://user-images.githubusercontent.com/13482005/151570749-4b2679f5-dd9c-4ebc-96d6-0b9e2cc937ed.png">

### _How was this patch tested?_
- [ ] Add some test cases that check the changes thoroughly including negative and positive cases if possible

- [ ] Add screenshots for manual tests if appropriate

- [ ] [Run test](https://kyuubi.apache.org/docs/latest/develop_tools/testing.html#running-tests) locally before make a pull request

Closes #1846 from link3280/improvement/new-issue-template.

Closes #1846

65c944fd [Paul Lin] Add checkboxes sections
05584f27 [Paul Lin] Add `improvement` issue template

Authored-by: Paul Lin <paullin3280@gmail.com>
Signed-off-by: Fei Wang <fwang12@ebay.com>

.github/ISSUE_TEMPLATE/improvement.yml

@@ -0,0 +1,76 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+# See https://gh-community.github.io/issue-template-feedback/structured/
+
+name: Kyuubi Improvement
+title: "[Improvement] "
+description: Suggest an improvement on performance, code quality, user experience, etc
+labels: [ "improvement" ]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Thank you for contributing to Apache Kyuubi! Your opinions are deeply valued by the community.
+
+  - type: checkboxes
+    attributes:
+      label: Code of Conduct
+      description: The Code of Conduct helps create a safe space for everyone. We require that everyone agrees to it.
+      options:
+        - label: >
+            I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)
+          required: true
+
+  - type: checkboxes
+    attributes:
+      label: Search before asking
+      options:
+        - label: >
+            I have searched in the [issues](https://github.com/apache/incubator-kyuubi/issues?q=is%3Aissue) and found no similar
+            issues.
+          required: true
+
+  - type: textarea
+    attributes:
+      label: What would you like to be improved?
+      placeholder: >
+        Please describe the problem you see and how it is needed to be improved.
+    validations:
+      required: true
+
+  - type: textarea
+    attributes:
+      label: How should we improve?
+      placeholder: >
+        Please provide the solution if you have thoughts.
+    validations:
+      required: false
+
+  - type: checkboxes
+    attributes:
+      label: Are you willing to submit PR?
+      description: >
+        A pull request is optional, but we are glad to help you in the contribution process
+        especially if you already know a good understanding of how to implement the fix.
+        Kyuubi is a community-driven project and we love to bring new contributors in.
+      options:
+        - label: Yes I am willing to submit a PR!
+
+  - type: markdown
+    attributes:
+      value: "Thanks for taking the time to create this improvement issue!"