fix: Add not_authorized to ResultEncoder

[jahands]

This fixes an exception being thrown by requests containing invalid auth.

Before, @upstash/redis would throw the following error when using invalid auth:
Error: SyntaxError: Unexpected end of JSON input
SRH logs also showed this error:

00:33:22.502 [error] #PID<0.1202.0> running Srh.Http.BaseRouter (connection #PID<0.1201.0>, stream id 1) terminated
Server: redis.uuid.rocks:80 (http)
Request: POST /
** (exit) an exception was raised:
** (FunctionClauseError) no function clause matching in Srh.Http.ResultEncoder.encode_response/1
(srh 0.1.0) lib/srh/http/result_encoder.ex:4: Srh.Http.ResultEncoder.encode_response({:not_authorized, "Invalid token"})
(srh 0.1.0) lib/srh/http/base_router.ex:36: Srh.Http.BaseRouter.do_command_request/2
(srh 0.1.0) lib/plug/router.ex:246: anonymous fn/4 in Srh.Http.BaseRouter.dispatch/2
(telemetry 1.1.0) /app/deps/telemetry/src/telemetry.erl:320: :telemetry.span/3
(srh 0.1.0) lib/plug/router.ex:242: Srh.Http.BaseRouter.dispatch/2
(srh 0.1.0) lib/srh/http/base_router.ex:1: Srh.Http.BaseRouter.plug_builder_call/2
(plug_cowboy 2.5.2) lib/plug/cowboy/handler.ex:12: Plug.Cowboy.Handler.init/2
(cowboy 2.9.0) /app/deps/cowboy/src/cowboy_handler.erl:37: :cowboy_handler.execute/2

After this PR, @upstash/redis throws the following:
SyntaxError: Unexpected token 'I', "Invalid token" is not valid JSON

This is a much more helpful client error, and cleans up the SRH logs (which no longer show anything with invalid auth errors.)

[hiett]

Thank you! Looks great. Hope you enjoyed your time with Elixir!