druid/.github/pull_request_template.md

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Fixes #XXXX.

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### Description

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<!-- Describe your patch: what did you change in code? How did you fix the problem? -->

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#### Fixed the bug ...
#### Renamed the class ...
#### Added a forbidden-apis entry ...

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In each section, please describe design decisions made, including:
 - Choice of algorithms
 - Behavioral aspects. What configuration values are acceptable? How are corner cases and error conditions handled, such as when there are insufficient resources?
 - Class organization and design (how the logic is split between classes, inheritance, composition, design patterns)
 - Method organization and design (how the logic is split between methods, parameters and return types)
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<hr>

This PR has:
- [ ] been self-reviewed.
   - [ ] using the [concurrency checklist](https://github.com/apache/druid/blob/master/dev/code-review/concurrency.md) (Remove this item if the PR doesn't have any relation to concurrency.)
- [ ] added documentation for new or modified features or behaviors.
- [ ] added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
- [ ] added or updated version, license, or notice information in [licenses.yaml](https://github.com/apache/druid/blob/master/licenses.yaml)
- [ ] added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
- [ ] added unit tests or modified existing tests to cover new code paths.
- [ ] added integration tests.
- [ ] been tested in a test Druid cluster.

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<hr>

##### Key changed/added classes in this PR
 * `MyFoo`
 * `OurBar`
 * `TheirBaz`