xDS test server: document rpc-behavior metadata, add hostname option (#29475)
xDS test server: document rpc-behavior metadata, add hostname option (#29475)

* xDS test server: document rpc-behavior metadata, add fail-on option

* Update to address suggestions

* Address more existing rpc-behavior values

* Address comments

* Address comments again
jtattermusch/grpc,ejona86/grpc,vjpai/grpc,vjpai/grpc,ejona86/grpc,vjpai/grpc,stanley-cheung/grpc,vjpai/grpc,ctiller/grpc,ejona86/grpc,ctiller/grpc,grpc/grpc,grpc/grpc,stanley-cheung/grpc,grpc/grpc,ctiller/grpc,jtattermusch/grpc,jtattermusch/grpc,grpc/grpc,stanley-cheung/grpc,ctiller/grpc,ejona86/grpc,jtattermusch/grpc,ctiller/grpc,jtattermusch/grpc,ejona86/grpc,jtattermusch/grpc,jtattermusch/grpc,jtattermusch/grpc,vjpai/grpc,grpc/grpc,stanley-cheung/grpc,stanley-cheung/grpc,ctiller/grpc,ejona86/grpc,stanley-cheung/grpc,ctiller/grpc,grpc/grpc,ejona86/grpc,ejona86/grpc,grpc/grpc,vjpai/grpc,stanley-cheung/grpc,vjpai/grpc,grpc/grpc,ctiller/grpc,vjpai/grpc,jtattermusch/grpc,vjpai/grpc,vjpai/grpc,ctiller/grpc,stanley-cheung/grpc,vjpai/grpc,jtattermusch/grpc,grpc/grpc,stanley-cheung/grpc,ejona86/grpc,ctiller/grpc,jtattermusch/grpc,ctiller/grpc,stanley-cheung/grpc,jtattermusch/grpc,ejona86/grpc,ctiller/grpc,grpc/grpc,grpc/grpc,ejona86/grpc,vjpai/grpc,ejona86/grpc,grpc/grpc,stanley-cheung/grpc,stanley-cheung/grpc