chore: add issue and pull request templates

.github/ISSUE_TEMPLATE/PULL_REQUEST_TEMPLATE.md

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+**Description**
+
+<!--
+If this PR is related to an open issue, please mention the issue below.
+-->
+
+This PR is related to #
+
+
+**Notes for Reviewers**
+
+<!--
+Thank you for contributing to Nighthawk! 
+
+Please read contributing guidelines https://github.com/envoyproxy/nighthawk/blob/master/CONTRIBUTING.md by following the community's contribution conventions upfront, the review process will be accelerated and your PR merged more quickly.
+-->

.github/ISSUE_TEMPLATE/bug.md

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+---
+name: Non-{crash,security} bug
+about: Bugs which are not crashes, DoS or other security issue
+title: ''
+labels: bug,triage
+assignees: ''
+
+---
+
+*Title*: *One line description*
+
+*Description*:
+>What issue is being seen? Describe what should be happening instead of
+the bug, for example: Nighthawk should not crash, the expected value isn't
+returned, etc.
+
+*Reproduction steps*:
+> Include sample requests, environment, etc. All data and inputs
+required to reproduce the bug.
+
+>**Note**: If there are privacy concerns, sanitize the data prior to
+sharing.
+
+*Logs*:
+>Include the Nighthawk logs.
+
+>**Note**: If there are privacy concerns, sanitize the data prior to
+sharing.
+
+*Call Stack*:
+> If the Envoy binary is crashing, a call stack is **required**.
+Please refer to the [Bazel Stack trace documentation](https://github.com/envoyproxy/envoy/tree/master/bazel#stack-trace-symbol-resolution).

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Suggest an idea for this project
+title: ''
+labels: enhancement,triage
+assignees: ''
+
+---
+
+*Title*: *One line description*
+
+*Description*:
+>Describe the the desired behavior, what scenario it enables and how it
+would be used.
+
+[optional *Relevant Links*:]
+>Any extra documentation required to understand the issue.