[feat] Split config into linting and formatting

[ShGKme]

Having linting mixed with formatting:

• Complicates migration because formatting brings dramatic changes with potentially thousands of errors
  • Having it split allows migration in 2 steps
• Restricts from using other tools for formatting
  • Such as Prettier or oxlint
• Is more opinionated in general

[susnux]

Having linting mixed with formatting

That was the conclusion, we discussed splitting formatting and linting e.g. when I proposed prettier.
But the consensus was that to enforce our codestyle and simplicity we should keep only ESLint.

Maybe it makes sense for non-nextcloud apps though, so maybe just export the createConfig method and add some more options to it.

[ShGKme]

I did not propose to remove formatting, but to split them to resolve the listed problems.

Also, conditions may change and do change. For example, there is oxc now, which can be used via Prettier for JS/TS files. One day it might probably support Vue as well.

We can provide both formatting and linting via ESLint config, but we can also provide flexibility to be more adaptive for different cases.

[susnux]

Restricts from using other tools for formatting

It was about this one, as its by design to enforce the Nextcloud formatting which is not possible with tools like prettier due to limited configuration options.