Update consumer-proguard-rules.pro for GSON (#230)

**Requirements**

- [x] I have added test coverage for new or changed functionality
- [x] I have followed the repository's [pull request submission
guidelines](../blob/main/CONTRIBUTING.md#submitting-pull-requests)
- [x] I have validated my changes against all supported platform
versions

**Related issues**

refs #219

**Describe the solution you've provided**

Update R8 config according to GSON docs
https://github.com/google/gson/blob/main/Troubleshooting.md#-illegalstateexception-typetoken-must-be-created-with-a-type-argument--runtimeexception-missing-type-parameter

**Describe alternatives you've considered**

n/a

**Additional context**

n/a

launchdarkly-android-client-sdk/consumer-proguard-rules.pro

@@ -32,6 +32,8 @@
 -keep class * implements com.google.gson.TypeAdapterFactory
 -keep class * implements com.google.gson.JsonSerializer
 -keep class * implements com.google.gson.JsonDeserializer
+-keep,allowobfuscation,allowshrinking class com.google.gson.reflect.TypeToken
+-keep,allowobfuscation,allowshrinking class * extends com.google.gson.reflect.TypeToken
 
 -dontwarn org.conscrypt.ConscryptHostnameVerifier