API Client Refactoring and Reliability Improvements

[mattdot]

This pull request includes several changes to improve the Power Platform Terraform Provider. The most important changes include adding Codecov integration, updating environment variables for VSCode, refining documentation, and refactoring the API client code.

CI/CD Improvements:

• Added a step to upload test coverage results to Codecov in the GitHub Actions workflow file .github/workflows/run_tests.yml.

Environment Configuration:

• Updated .vscode/launch.json to set the TF_ACC environment variable to true for enabling Terraform acceptance tests.

Documentation Updates:

• Updated the README.md and docs/index.md to remove redundant warnings about using the provider in production environments. [1] [2]
• Changed the type of the expected_http_status field from List of Number to Set of Number in several documentation files to reflect the correct data type. [1] [2] [3] [4] [5]
• Added a new docs/guides/release_notes.md file to document breaking changes and major features for each release.

Code Refactoring:

• Refactored the API client code by moving it from internal/api/api_client.go to internal/api/client.go, improving the structure and adding detailed comments. [1] [2]
• Renamed internal/api/api_client_test.go to internal/api/client_test.go and updated imports to reflect the new structure.

[codecov-commenter]

Welcome to Codecov :tada:

Once you merge this PR into your default branch, you're all set! Codecov will compare coverage reports and display results in all future pull requests.

Thanks for integrating Codecov - We've got you covered :open_umbrella: