Setting min sdk to 21

[LikeTheSalad]

To align with OTel Android

[ubaierbhat]

Please note (0.14.0) crashes the application on applications on SDK 24 (even if we skip agent initialisation for the this SDK level)

java.lang.ClassNotFoundException - Didn't find class "java.time.Instant" on path: DexPathList[[zip file "/data/app/com.omniva.omnigo.debug-1/base.apk"],nativeLibraryDirectories=[/data/app/com.omniva.omnigo.debug-1/lib/arm, /data/app/com.omniva.omnigo.debug-1/base.apk!/lib/armeabi-v7a, /syst

ConnectionErrorSpanInterceptor.java:36

[LikeTheSalad]

Thank you for your feedback @ubaierbhat

It seems like the OTel SDK is still getting some of its classes loaded even if the code that references them is not executed at runtime. If that's the case, however, by the time this work is done and the Elastic Agent min sdk is set to 21, I don't think that would make this issue go away unfortunately, because the OTel Java SDK still uses API 21+ tools that can only be covered by Android's corelib desugaring artifacts. So our recommendation is to add Android's desugaring libs to any project that has a minSdk lower than 26.