Migrate to ESLint major version `8`

[svengreb]

The currently supported ESLint major version for all npm packages of this styleguide is still 7 which has been updated to 8, released on 2021-10-09.
To update all packages, the official ESLint 8 migration guide will be used to adapt the breaking changes for users, but none of them affects this project so there are no further steps required other than updating the corresponding package (dev/peer)dependencies.

The following plugins will be updated to their latest major & minor versions to match the supported ESLint version:

• eslint — ^7.32.0 → major version 8 · currently latest version is ^8.39.0 which will be used as minimal requirement.
• eslint-plugin-prettier — ^3.4.1 → major version 4 · currently latest version is 4.2.1 which will be used as minimal requirement.
  • Dropped support for older versions of ESLint, Prettier and Node. It now requires at least ESLint >=7.28.0 <8.0.0, Prettier >=2.0.0 <3.0.0 and Node >=12.0.0.
• eslint-find-rules — 3.6.1 → major version 4 · currently latest version is 4.1.0 which will be used as minimal requirement.
  • Comes with support for ESLint 8.
• @typescript-eslint/eslint-plugin — ^4.33.0 → major version 5 · currently latest version is 5.59.1 which will be used as minimal requirement.
  • Comes with support for ESLint 8.
  • Dropped support for Node <=10.
  • Dropped support for ESLint <=5.
• @typescript-eslint/parser — ^4.33.0 → major version 5 · currently latest version is 5.59.1 which will be used as minimal requirement.
  • Comes with support for ESLint 8.
  • Dropped support for Node <=10.
  • Dropped support for ESLint <=5.
• typescript — ^4.9.5 → major version 5 · currently latest version is 5.0.4 which will be used as minimal requirement.
  • Dropped support for Node <=12.