Improve Kover setup by using only convention plugins (#6213)

* Improve Kover setup using convention plugins.
* Add a new JVM library convention plugin with Kover support

plugins/src/main/kotlin/io.element.android-root.gradle.kts

@@ -1,7 +1,7 @@
-import extension.applyKoverPluginToAllSubProjects
+import extension.setupKover
 
 plugins {
     id("org.jetbrains.kotlinx.kover") apply false
 }
 
-applyKoverPluginToAllSubProjects()
+setupKover()