MinSDKVersion is set to 28 even when cronet itself supports versions from SDK JellyBean

[petrnymsa]

Is there a specific reason why minSdkVersion is set to 28? See https://github.com/dart-lang/http/blob/73b0b1c9ef2964c4619fd23068b8f60292e902c6/pkgs/cronet_http/android/build.gradle#L53C4-L53C25

According to https://github.com/GoogleChromeLabs/cronet-sample/blob/master/android/app/build.gradle, cronet itself supports even JellyBean (SDK 18).

In our apps, we have support for SDK >24, and we cant simply increase it as we support over 1M+ users.

[AlexV525]

Also 26e55c3#r135553689

[petrnymsa]

When we can expect next release? @brianquinlan