Allow a user choose a path when a Thrift/gRPC service has more than two paths.

[trustin]

For example, a user can bind the same Thrift service at two different paths with some minor differences (e.g. decorators):

HelloService.AsyncIface hello = ...;
Server server = Server.builder()
                      .service("/a", THttpService.of(hello))
                      .service("/b", THttpService.of(hello).decorate(...))
                      .build();

In that case, currently, in DocService UI, a user cannot choose which path (/a or /b) a request should be sent to. We could show some drop-down list so that a user can choose among the available paths.

/cc @linna-li

[trustin]

Thanks again @linna-li for reporting this issue and @kojilin for fixing it the right way.