Use Netty's DefaultThreadFactory instead of Guava's ThreadFactoryBuilder.
Use Netty's DefaultThreadFactory instead of Guava's ThreadFactoryBuilder.

So far, we have passed a custom Executor to the NioEventLoopGroup constructor,
in order to get custom thread names and be compatible with both Netty 4 and
Netty 5. However, Netty 5 is no more (RIP) and Netty's DefaultThreadFactory
includes some optimizations around thread local storage, that Guava's executor
does not have.

The thread names will be a bit different, as DefaultThreadExecutor additionally
puts in the thread pool id after the name prefix.

For example:

Before:
grpc-default-boss-ELG-0
grpc-default-worker-ELG-0
grpc-default-worker-ELG-1

After:
grpc-default-boss-ELG-0-0
grpc-default-worker-ELG-1-0
grpc-default-worker-ELG-1-1

grpc/grpc-java,ejona86/grpc-java,anuraaga/grpc-java,rmichela/grpc-java,LuminateWireless/grpc-java,simonhorlick/grpc-java,grpc/grpc-java,louiscryan/grpc-java,pieterjanpintens/grpc-java,zpencer/grpc-java,zhangkun83/grpc-java,nmittler/grpc-java,dapengzhang0/grpc-java,carl-mastrangelo/grpc-java,rmichela/grpc-java,pieterjanpintens/grpc-java,stanley-cheung/grpc-java,rmichela/grpc-java,zpencer/grpc-java,carl-mastrangelo/grpc-java,LuminateWireless/grpc-java,anuraaga/grpc-java,dapengzhang0/grpc-java,zpencer/grpc-java,dapengzhang0/grpc-java,elandau/grpc-java,louiscryan/grpc-java,simonhorlick/grpc-java,nmittler/grpc-java,louiscryan/grpc-java,stanley-cheung/grpc-java,nmittler/grpc-java,zpencer/grpc-java,zhangkun83/grpc-java,simonhorlick/grpc-java,zhangkun83/grpc-java,ejona86/grpc-java,dapengzhang0/grpc-java,ejona86/grpc-java,grpc/grpc-java,elandau/grpc-java,simonhorlick/grpc-java,ejona86/grpc-java,rmichela/grpc-java,anuraaga/grpc-java,stanley-cheung/grpc-java,zhangkun83/grpc-java,elandau/grpc-java,elandau/grpc-java,LuminateWireless/grpc-java,pieterjanpintens/grpc-java,stanley-cheung/grpc-java,carl-mastrangelo/grpc-java,carl-mastrangelo/grpc-java,pieterjanpintens/grpc-java,grpc/grpc-java