Add Get Order operation to the Order Capability

[mathieulag]

Description

Draft spec for the Get Order operation to the Order Capability, expending on the concept of the Order Event webhook.

Type of change

• New feature (non-breaking change which adds functionality)
• Documentation update

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Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

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Pull Request Title

This repository enforces Conventional Commits. Your PR title must follow
this format: type: description or type!: description for breaking changes.

Types:

• feat: A new feature
• fix: A bug fix
• docs: Documentation only changes
• style: Changes that do not affect the meaning of the code (white-space,
  formatting, etc)
• refactor: A code change that neither fixes a bug nor adds a feature
• perf: A code change that improves performance
• test: Adding missing tests or correcting existing tests
• chore: Changes to the build process or auxiliary tools and libraries

Breaking Changes:

If your change is a breaking change (e.g., removing a field or file), you
must add ! before the colon in your title:
type!: description

Examples:

• feat: add new payment gateway
• fix: resolve crash on checkout
• docs: update setup guide
• feat!: remove deprecated buyer field from checkout