Updated issue templates (#3590)

Adding the following templates:
- Feature / Enhancement
- Question
- Generic issue

.github/ISSUE_TEMPLATE/feature---enhancement-request.md

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+---
+name: Feature / Enhancement request
+about: Suggest an improvement for this project
+title: ''
+labels: enhancement
+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/ISSUE_TEMPLATE/other.md

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+---
+name: Other
+about: Create a generic Github issue
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+

.github/ISSUE_TEMPLATE/question.md

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+---
+name: Question
+about: As a question about KSQL
+title: ''
+labels: question
+assignees: ''
+
+---
+
+**Search for existing answers**
+Many questions have been asked before.  Please have a quick search to see if there is already an answer to your question.  There are two main resources for finding answers:
+
+1. [Existing KSQL Github issues, including _closed_ issues](https://github.com/confluentinc/ksql/issues?utf8=%E2%9C%93&q=is%3Aissue+)
+1. [KSQL on Stack Overflow](https://stackoverflow.com/questions/tagged/ksql)
+
+If you can't see an answer to your question, then please raise a new Github or Stack overflow issue.
+
+**Provide details of the setup you're running**
+Let us know what version of KSQL you're running, what OS, etc, 
+
+**Outline your question**
+Ask you question!