feat: Multiplatform OFREP provider

[bencehornak]

This PR

Implements an OFREP provider for Kotlin Multiplatform. The implementation was initially based on @thomaspoignant's OFREP implementation, then I made a bunch of changes to make it compatible with multiple platforms:

• Replaced Java APIs with Kotlin APIs
• Replaced jUnit with kotlin-test
• Replaced OkHttp with Ktor
• Replaced GSON with kotlinx-serialization
• Replaced the Java Timer with Kotlin Coroutines
• ...

Now the project is compatible with multiple platforms, and can be easily extended to other ones by changing the targets in the build.gradle.kts:

Supported	Platform	Supported versions
✅	Android
✅	JVM	JDK 11+
✅	Native	Linux x64
❌	Native	Other native targets
✅	Javascript (Node.js)
✅	Javascript (Browser)
❌	Wasm

Notes

I have based these changes on the unmerged open-feature/kotlin-sdk#148, which brings in multiplatform support for the SDK.

Prerequisites

• Merge feat!: Kotlin Multiplatform support kotlin-sdk#148 first

How to test

1. Check out my PR in the Kotlin SDK repo: feat!: Kotlin Multiplatform support kotlin-sdk#148
2. Publish the SDK locally as 0.5.0 - I have made the following changes to be able to do so:

diff --git a/build.gradle.kts b/build.gradle.kts
index dbeedff..122dbf0 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -11,7 +11,7 @@ plugins {
 allprojects {
     extra["groupId"] = "dev.openfeature"
 // x-release-please-start-version
-    ext["version"] = "0.4.1"
+    ext["version"] = "0.5.0"
 // x-release-please-end
 }
 group = project.extra["groupId"].toString()
diff --git a/kotlin-sdk/build.gradle.kts b/kotlin-sdk/build.gradle.kts
index 6cc9db9..437d2b6 100644
--- a/kotlin-sdk/build.gradle.kts
+++ b/kotlin-sdk/build.gradle.kts
@@ -3,7 +3,7 @@ plugins {
     id("com.android.library")
     id("org.jetbrains.kotlin.multiplatform")
     id("maven-publish")
-    id("signing")
+//    id("signing")
     id("org.jlleitschuh.gradle.ktlint")
     id("org.jetbrains.kotlinx.binary-compatibility-validator")
 }
@@ -129,7 +129,6 @@ publishing {
         }
     }
 }
-
-signing {
-    sign(publishing.publications["release"])
-}
\ No newline at end of file
+//signing {
+//    sign(publishing.publications["release"])
+//}

3. Run the tests on all platforms with ./gradlew -p providers/ofrep allTests
4. You might need to meet some prerequisites to have the tests pass for all platforms