Fix: Improve Gradle build configuration

[martinfkaeser]

Hi,

First off, thank you for creating and maintaining routekit! I really like the library, especially its elegance and ease of use.

I tried to import routekit into my project via Jitpack, but the build failed because it defaulted to an older JDK version (see build log: https://jitpack.io/com/github/maxim5/routekit/v0.2.0/build.log). It appears the minimum required Java version was not specified in the build.gradle file.

To address this and make the build process a bit smoother, I've made the following improvements to the Gradle configuration:

1. Set Java Version: Explicitly set the required Java version to 17 in build.gradle.
2. Add Maven Publish Plugin: Included the maven-publish plugin to enable local publishing with gradlew publishToMavenLocal.
3. Add Gradle Wrapper: Added the Gradle wrapper (gradlew scripts and associated files) to provide a more convenient and consistent build experience.

I hope you find these changes helpful. Thanks again for your great work on this library!

Best regards,
Martin