Issue title: Fix blaze websocket server example
 Issue body: If I run the websocket server example for blaze from the `examples-blaze` sub-project

`runMain com.example.http4s.blaze.BlazeWebSocketExample`

and point the [websocket.org echo client](http://www.websocket.org/echo.html) at it, it fails during connection with the following error:

```
[NIO1SocketServerChannelFactory] INFO  o.h.blaze.channel.ServerChannelGroup - Connection to /38d1:d2b4:3d06:83e8:96a5:8c2:893d:aba5:59297 accepted at Tue Jun 23 13:29:03 PDT 2015.
[info] 13:29:04.286 [pool-1-thread-1] INFO  org.http4s.blaze.pipeline.Stage - Unknown connection header: 'Upgrade'. Closing connection upon completion.
```

For control, I spun up a sample [Unfiltered](https://github.com/unfiltered/unfiltered) websocket server and did the same thing, and it worked as expected.

 Comments: 
 Comment 0: Works for me! Are you using the latest master? What is the url you're connecting with? `ws://localhost:8080/http4s/wsecho` and `ws://localhost:8080/http4s/ws` both work for me. What browser are you using? I've tested with current Chrome and Firefox.
 Comment 1: @bryce-anderson It works for me too. I was using the wrong url, missing the `http4s` part.

Sorry about that.

 Comment 2: I am getting the same error but using the right url according to the above?

```
2021-05-22 18:14:42,930 [ioapp-compute-0] INFO  o.h.b.c.nio1.NIO1SocketServerGroup - Service bound to address /116.69.203.115:8081
2021-05-22 18:14:42,938 [ioapp-compute-0] INFO  o.h.server.blaze.BlazeServerBuilder - 
  _   _   _        _ _
 | |_| |_| |_ _ __| | | ___
 | ' \  _|  _| '_ \_  _(_-<
 |_||_\__|\__| .__/ |_|/__/
             |_|
2021-05-22 18:14:43,035 [ioapp-compute-0] INFO  o.h.server.blaze.BlazeServerBuilder - http4s v0.21.23 on blaze v0.14.16 started at http://116.69.203.115:8081/
2021-05-22 18:14:52,011 [blaze-selector-0] INFO  o.h.b.c.nio1.NIO1SocketServerGroup - Accepted connection from /116.69.203.115:50508
2021-05-22 18:14:52,323 [ioapp-compute-1] INFO  o.h.s.blaze.Http1ServerStage$$anon$1 - Unknown connection header: 'Upgrade'. Closing connection upon completion.
```

URL: `ws://localhost:8081/http4s/ws`
 Comment 3: I can reproduce this.  It's probably a different issue than 2015, but the context is here, so I'll just reopen this one.
 Comment 4: Thanks. I've determined that the `http4s` prefix is definitely wrong for 0.21, but even when the request reaches the route, this is always logged:

```
2021-05-22 22:12:54,890 [blaze-selector-2] INFO  o.h.b.c.nio1.NIO1SocketServerGroup - Accepted connection from /38d1:d2b4:3d06:83e8:96a5:8c2:893d:aba5:59264
2021-05-22 22:12:54,891 [ioapp-compute-5] INFO  o.h.s.blaze.Http1ServerStage$$anon$1 - Unknown connection header: 'Upgrade'. Closing connection upon completion.

```
 Comment 5: :+1: I was just looking at the code and trying it without and it works. Thanks for testing!
 Comment 6: I think one of the difficulties I had is that I am testing a client impl at the same time. The moral here is to use a known-good client test tool and debug only one side at a time! 🙄 
{'source': 'GithubIssues', 'repo_name_with_owner': 'http4s/http4s', 'issue_id': 90490072, 'repo_stars': 2338.0}