Include valid proguard config in java protolite library

[yschimke]

Related to

https://issuetracker.google.com/issues/144631039
and
#6463

What language does this apply to?

Java Protolite

Describe the problem you are trying to solve.

Include necessary proguard definitions to avoid failures in release builds.

Describe the solution you'd like

Include https://github.com/protocolbuffers/protobuf/blob/520c601c99012101c816b6ccc89e8d6fc28fdbb8/java/lite/proguard.pgcfg in the library, so it's applied automatically.

See https://github.com/square/okhttp/blob/master/docs/features/r8_proguard.md for how this feature works in other libraries

https://raw.githubusercontent.com/square/okhttp/master/okhttp/src/jvmMain/resources/META-INF/proguard/okhttp3.pro

Describe alternatives you've considered

Currently every app needs to fail initially, search for the error message and include the same fix.

[googleberg]

I'm happy to review a Pull Request for this issue.

[yschimke]

For discussion #11313