Created issue templates (#622)

* Created issue templates

Added bug, feature, improvement and milestone issues templates.

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Create a report to help us improve
+title: 'bug:'
+labels: ''
+assignees: ''
+
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+Steps to reproduce the behavior:
+1. Go to '...'
+2. Click on '....'
+3. Scroll down to '....'
+4. See error
+
+**Expected behavior**
+A clear and concise description of what you expected to happen.
+
+**Screenshots**
+If applicable, add screenshots to help explain your problem.
+
+**Desktop (please complete the following information):**
+ - OS: [e.g. iOS]
+ - Browser [e.g. chrome, safari]
+ - Version [e.g. 22]
+
+### go-waku version/commit hash
+State the version of `go-waku` where you've encountered the bug or, if built off a specific commit, the relevant commit hash. You can check the version by running `./build/waku --version`.
+- e.g. `v0.7.0` or `e21bdab`
+
+**Additional context**
+Add any other context about the problem here.

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Suggest an idea for go-waku implementation
+title: 'feat:'
+labels: ''
+assignees: ''
+
+---
+
+### Problem
+A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
+
+### Suggested solution
+A clear and concise description of what you want to happen.
+
+### Alternatives 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.
+
+### Acceptance criteria
+A list of tasks that need to be done for the issue to be considered resolved.

.github/ISSUE_TEMPLATE/improvement.md

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+---
+name: Improvement
+about: Suggest improvements to the codebase or processes. This includes refactoring,
+  docs and any other chores
+title: 'chore:'
+labels: ''
+assignees: ''
+
+---
+
+### Background
+A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]; There is a spelling error in [...]; It's difficult to read the code in module [...]
+
+### Details
+A clear and concise description of what you want to happen.
+
+### Acceptance criteria
+A list of tasks that need to be done for the issue to be considered resolved.

.github/ISSUE_TEMPLATE/milestone-issue-template.md

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+---
+name: Milestone Issue Template
+about: Track Milestones
+title: "[Milestone] "
+labels: milestone
+assignees: ''
+
+---
+
+<!-- Please ensure you are assigning the matching epic label to the milestone -->
+<!-- All _active_ (being worked on) milestones MUST have an owner (GitHub assignee) -->
+
+**Planned start date**:
+**Due date**:
+
+# Summary
+
+<!-- Provide a high level summary of the Milestone -->  
+
+# Acceptance Criteria
+
+<!-- describe the deliverable of this milestone and its attributes in plain English -->
+
+## Tasks
+
+<!--
+Breakdown of the work
+- [ ] Task 1
+- [ ] Link to GitHub issue tracking task 2
+-->
+
+# RAID (Risks, Assumptions, Issues and Dependencies)
+
+<!-- List dependencies on other milestones (avoid dependencies on tasks) -->
+
+<!-- List dependencies on other teams -->
+
+<!-- List any risks or assumptions that will be cleared as work progresses -->
+
+<!-- List any GitHub issues that tracks any blocker or any of the items above -->