Add tutorial for converting existing projects

I am thinking about including a markdown tutorial of how to add the schematics, packages, and configs to an existing Angular project.

- cross link to existing configuration files to save time and prevent duplicate information
- add new `lint:summary` and `lint:style:summary` scripts that show a count of errors/warnings per rule
- I've used [eslint-formatter-summary](https://github.com/mhipszki/eslint-formatter-summary) for this in the past, but I fear it may not be compatible with eslint 9.