xds_e2e_test_lib: increase default timeouts in test framework (#30756)
xds_e2e_test_lib: increase default timeouts in test framework (#30756)

* e2e tests: add test scaling factor to durations in channel args

* apply test scaling factor when encoding durations in xDS protos

* apply scaling factor in fixed timeout in WaitForNack()

* fix overflow

* clang-format

* adjust timeouts in fault injection tests

* add missing slowdown factor

* clang-format

* xds_e2e_test_lib: increase default timeouts in test framework
stanley-cheung/grpc,grpc/grpc,grpc/grpc,jtattermusch/grpc,jtattermusch/grpc,grpc/grpc,grpc/grpc,jtattermusch/grpc,stanley-cheung/grpc,stanley-cheung/grpc,jtattermusch/grpc,grpc/grpc,stanley-cheung/grpc,stanley-cheung/grpc,stanley-cheung/grpc,jtattermusch/grpc,jtattermusch/grpc,jtattermusch/grpc,stanley-cheung/grpc,grpc/grpc,grpc/grpc,stanley-cheung/grpc,grpc/grpc,stanley-cheung/grpc,jtattermusch/grpc,grpc/grpc,stanley-cheung/grpc,jtattermusch/grpc,grpc/grpc,jtattermusch/grpc,stanley-cheung/grpc,stanley-cheung/grpc,grpc/grpc,jtattermusch/grpc,jtattermusch/grpc,grpc/grpc