MPT-16808: add CodeRabbit config and copilot-instructions (#184)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

Closes [MPT-16808](https://softwareone.atlassian.net/browse/MPT-16808)

- Introduce `.coderabbit.yaml` configuration file with schema definition
and remote configuration reference
- Add comprehensive Python coding guidelines and workflow instructions
in `.github/workflows/copilot-instructions.md`, covering conventions for
type hints, docstrings, testing practices, linting standards, and
development workflow
- Remove the Danger GitHub Actions workflow
(`.github/workflows/danger.yml`)

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

[MPT-16808]:
https://softwareone.atlassian.net/browse/MPT-16808?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

Author: d3rky

.coderabbit.yaml

@@ -0,0 +1,3 @@
+# yaml-language-server: $schema=https://coderabbit.ai/integrations/schema.v2.json
+remote_config:
+  url: "https://raw.githubusercontent.com/softwareone-platform/swo-extension-playground/refs/heads/main/.coderabbit.yaml"

.github/workflows/copilot-instructions.md

@@ -0,0 +1,43 @@
+---
+description: 'Python coding conventions and guidelines'
+applyTo: '**/*.py'
+---
+
+# Python Coding Conventions
+
+## General Instructions
+- All configuration **must be provided via environment variables**.
+- Do not hardcode configuration values.
+- Write maintainable, readable, and predictable code.
+- In `pyproject.toml`:
+  - Use `*` for **minor versions only**
+    ✅ `django==4.2.*`
+    ❌ `django==^4.2.2`
+
+- Use consistent naming conventions and follow language-specific best practices.
+
+## Python Instructions
+- Use type annotations (PEP 484) - except in the `tests/` folder.
+- All public functions, methods, and classes **must include [Google-style docstrings](https://google.github.io/styleguide/pyguide.html)**.
+- **Do not add inline comments**; rely on clear code and docstrings instead.
+- Function and variable names must be explicit and intention-revealing.
+- `pyproject.toml` is the source of truth for code quality rules. Generated code must not violate any configured rules.
+- **ruff** is the primary linter for general Python style and best practices.
+- **flake8** is used exclusively to run:
+  - `wemake-python-styleguide` - Enforces strict Python coding standards ([docs](https://wemake-python-styleguide.readthedocs.io/en/latest/))
+  - `flake8-aaa` - Validates the AAA pattern in tests
+- Follow PEP 8 unless explicitly overridden by ruff.
+- Prefer simple, explicit code over clever or compact implementations.
+
+## Testing
+- Use pytest only.
+- Tests must be written as **functions**, not classes.
+- Test files and functions must use the `test_` prefix.
+- Follow ***AAA(Arrange - Act - Assert)*** strictly. See the [flake8-aaa documentation](https://flake8-aaa.readthedocs.io/en/stable/index.html).
+- Do **not** use `if` statements or branching logic inside tests.
+- Prefer fixtures over mocks whenever possible.
+- Avoid duplicating test logic; extract shared setup into fixtures.
+- Use `mocker` only when mocking is unavoidable.
+- Never use `unittest.mock` directly.
+- Always use `spec` or `autospec` when mocking.
+- Use `@pytest.mark.parametrize` tests when testing permutations of the same behavior.