chore: modernize static files

[drupol]

Remove docker, add Nix files, update composer.json, remove scrutinizer, reformat files

This PR

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Related to #.
Fixes #.

[what-the-diff]

• Added .envrc
• Updated the editorconfig to match my personal preferences
• Changed some settings in auto-changelog config file (output, template)
• Removed scrutinizer and travis files as they are not needed anymore with github actions workflows
• Fixed a typo in CODE_OF_CONDUCT file: "behaviour" -> "behavior"
• Update to PHP 8.1
• Add Github actions for tests and release
• Remove docker-compose, use auto-changelog directly instead of a container (easier)
• Use prettier with proseWrap: always option to keep the changelogs readable in github diffs/commits view without having to scroll horizontally too much :)
• The imports section was changed to use the resource keyword instead of a string.
• In grumphp, extra_tasks were moved from root level to tasks and indentation was fixed for all parameters in this file.
• infection json: source directories is now an array with one element (instead of two). Also testFramework key has been removed as it's not needed anymore since we're using phpspec by default anyway so no need to specify that again here!
• phpspec yml: format and output keys are now arrays with multiple elements each (instead of just strings) - also they have been indented properly under extensions -> CodeCoverageExtension which wasn't done before either!