Modernize Gradle build scripts

[pvannierop]

Description:

This PR will update the Gradle build scripts to current best practices.

Included changes

• Upgrade to gradle 8.7
• Translate Groovy DSL to Kotlin DSL
• Implement Grdle version catalog
• Implement ktlint
• Fix kotlin code fomatting problems
• Implement a 'project convention plugin' (see https://docs.gradle.org/current/userguide/sharing_build_logic_between_subprojects.html#sec:convention_plugins_vs_cross_configuration)
• Translate remaining Java files into Kotlin

Checklist:

• [ ] The Main workflow has succeeded
• [ ] The Gatling tests have passed
• [ ] I have logged into the portal running locally with default admin credentials
• [ ] I have updated the README files if this change requires documentation update
• [ ] I have commented my code, particularly in hard-to-understand areas