Update issue templates

.github/ISSUE_TEMPLATE/01_bug.yaml

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+name: Bug Report
+description: Something is not working
+labels: [bug]
+body:
+  - type: textarea
+    id: description
+    attributes:
+      label: Description
+      placeholder: Please include steps to reproduce your issue, provide example code snippets if possible
+    validations:
+      required: true
+  - type: textarea
+    id: expected
+    attributes:
+      label: Expected Behaviour
+      placeholder: What did you expect to happen instead
+    validations:
+      required: true
+  - type: input
+    id: stdlib-version
+    attributes:
+      label: Version of stdlib
+      placeholder: 86ed2f3af570e2e09bdf03f1b74cdc4c4b13b43d, ...
+    validations:
+      required: true
+  - type: input
+    id: platform
+    attributes:
+      label: Platform and Architecture
+      placeholder: MacOS/ARM, Windows, OpenBSD, ...
+    validations:
+      required: true
+  - type: textarea
+    id: additional
+    attributes:
+      label: Additional Information
+      placeholder: Further relevant context, i.e. links to other issues
+    validations:
+      required: false

.github/ISSUE_TEMPLATE/02_proposal.yaml

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+name: Feature Proposal
+description: Suggestion for new functionality in stdlib
+labels: [idea]
+body:
+  - type: textarea
+    id: motivation
+    attributes:
+      label: Motivation
+      placeholder: |
+        What is the purpose of this proposal. Please provide usage examples for the new functionality as well.
+    validations:
+      required: true
+  - type: textarea
+    id: prior-art
+    attributes:
+      label: Prior Art
+      placeholder: |
+        Include links and references to other package manager or build systems if available.
+    validations:
+      required: false
+  - type: textarea
+    id: additional
+    attributes:
+      label: Additional Information
+      placeholder: Further relevant context, i.e. links to other issues
+    validations:
+      required: false
+

.github/ISSUE_TEMPLATE/03_free.md

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+---
+name: Free Form
+about: If the topic doesn't fit anything above and is not suitable for the lists below
+---

.github/ISSUE_TEMPLATE/config.yaml

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+contact_links:
+  - name: Stdlib discussion board
+    url: https://github.com/fortran-lang/stdlib/discussions
+    about: Discussion about stdlib related topics
+  - name: Fortran-lang discourse
+    url: https://fortran-lang.discourse.group/
+    about: Discussion about all things Fortran
+  - name: Fortran-lang mailing list
+    url: https://groups.io/g/fortran-lang
+    about: Mailinglist for the Fortran language