Update ESLint configuration

[seia-soto]

This PR:

• migrates eslint configuration to flat config respecting existing setup
• imports recommended default of prettier and typescript linter configs
• adds missing types for some files (replaces any)

There's a huge change in lib/consentomatic/tools.ts to support types properly. However, I could not fill all types up in consentomatic part as I lack some knowledge about the library internals. I added an eslint exception for those parts at this time and expect to fix in the future.