Introduce rectorphp / rector in CI Pipeline

[k911]

Is your feature request related to a problem? Please describe.
Introduce rectorphp/rector in CI Pipeline to handle coding standards

Describe the solution you'd like
Step in CI pipeline (CircleCI/CodeClimate), handled for example like run-static-analysis (phpstan)

Describe alternatives you've considered
I thought that PHP-CS-Fixer would handle that, but unfortunately, it can't format variable/method names to be in camelCase

Additional context
See: https://github.com/rectorphp/rector#how-to-apply-coding-standards