Fix `jvmTarget` & `ktlint` config in `kotlin` flag preset

[ks-yim]

Motivation:

• #133

Modifications:

• Use javaTargetCompatibility property value for kotlin compile JVM target.
• Use org.jlleitschuh.gradle.ktlint plugin's default ktlint version.
• Fix ktlint filter exclude condition for gen-src so that it can properly exclude dynamically attached sources.

[ks-yim]

It seems impossible to upgrade ktlint version without re-formatting many kotlin code in Armeria.

Testing the change in https://github.com/line/armeria/pull/4488.

[ikhoon]

It seems it's impossible to upgrade ktlint version without re-formatting many kotlin code in Armeria.

It is necessary, let’s re-format the Kotlin code and upgrade ktlint version.

[minwoox]

let’s re-format the Kotlin code and upgrade ktlint version.

+1 Let's re-format everything. 😄 @ks-yim Are you going to finish this up? or we can take it. 😄

[ks-yim]

@minwoox I can start working on this after a few days (maybe this weekend😊). Let me handle this.

[minwoox]

Let me merge this. Thanks a lot, @ks-yim 🙇