Upgrade to Kotlin 2.0

[bobeal]

Some resources:

• https://blog.jetbrains.com/kotlin/2024/05/celebrating-kotlin-2-0-fast-smart-and-multiplatform
• https://kotlinlang.org/docs/whatsnew20.html

Notes:

• Try the new k2 compiler before upgrading (https://kotlinlang.org/docs/k2-compiler-migration-guide.html)
• Check compatibility with Spring
• Probably, there will be a release of Arrow 2.0 quite soon now (and check if current version is compatible with Kotlin 2.0)