[Bug]: Cannot modify kv pairs after watch them in etcdctl

[Phoenix500526]

Description about the bug

1. One-line summary
   I cannot modify an existing key after using the etcdctl watch command to watch it.

2. What did I expect to happen?
   I should have successfully modified an existing key-value pair whether I watch it or not.

3. How to reproduce this issue?
   step 1. build an environment (run the quick_start.sh script)
   step 2. refer to the Relevant log output down below.

Version

0.1.0 (Default)

Relevant log output

1. Modified an existing key without watching it, all modified ops can work properly.
$ docker exec -it node4 bash
root@e97cceaf264a:/# alias etcdctl='/usr/local/bin/etcdctl --endpoints="http://172.20.0.3:2379"'
root@e97cceaf264a:/# etcdctl put hello world1
OK
root@e97cceaf264a:/# etcdctl put hello world2
OK
root@e97cceaf264a:/# etcdctl put hello world3
OK
root@e97cceaf264a:/# etcdctl put hello world4
OK
root@e97cceaf264a:/# etcdctl put hello world5
OK
root@e97cceaf264a:/# etcdctl put hello world6
OK
root@e97cceaf264a:/# etcdctl put hello world7
OK
root@e97cceaf264a:/# etcdctl put hello world8
OK
root@e97cceaf264a:/# etcdctl put hello world9
OK
root@e97cceaf264a:/# etcdctl put hello world10
OK

2. Modified an existing key after watching it, the most ops after the watch op failed.
$ docker exec -it node4 bash
root@2cb3d250295f:/# alias etcdctl='/usr/local/bin/etcdctl --endpoints="http://172.20.0.3:2379"'
root@2cb3d250295f:/# etcdctl put hello world1
OK
root@2cb3d250295f:/# etcdctl put hello world2
OK
root@2cb3d250295f:/# etcdctl put hello world3
OK
root@2cb3d250295f:/# etcdctl put hello world4
OK
root@2cb3d250295f:/# etcdctl put hello world5
OK
root@2cb3d250295f:/# etcdctl watch hello -w=json --rev=1
{"Header":{"revision":6},"Events":[{"kv":{"key":"aGVsbG8=","create_revision":2,"mod_revision":2,"version":1,"value":"d29ybGQx"}},{"kv":{"key":"aGVsbG8=","create_revision":2,"mod_revision":3,"version":2,"value":"d29ybGQy"}},{"kv":{"key":"aGVsbG8=","create_revision":2,"mod_revision":4,"version":3,"value":"d29ybGQz"}},{"kv":{"key":"aGVsbG8=","create_revision":2,"mod_revision":5,"version":4,"value":"d29ybGQ0"}},{"kv":{"key":"aGVsbG8=","create_revision":2,"mod_revision":6,"version":5,"value":"d29ybGQ1"}}],"CompactRevision":0,"Canceled":false,"Created":false}
^C
root@2cb3d250295f:/# etcdctl put hello world6
OK
root@2cb3d250295f:/# etcdctl put hello world7
OK
root@2cb3d250295f:/# etcdctl put hello world8
{"level":"warn","ts":"2023-01-14T03:29:53.423Z","logger":"etcd-client","caller":"v3/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc000244000/172.20.0.3:2379","attempt":0,"error":"rpc error: code = Unknown desc = malformed header: missing HTTP content-type"}
Error: rpc error: code = Unknown desc = malformed header: missing HTTP content-type
root@2cb3d250295f:/# etcdctl put hello world9
{"level":"warn","ts":"2023-01-14T03:30:01.802Z","logger":"etcd-client","caller":"v3/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc0001f6a80/172.20.0.3:2379","attempt":0,"error":"rpc error: code = Unknown desc = malformed header: missing HTTP content-type"}
Error: rpc error: code = Unknown desc = malformed header: missing HTTP content-type
root@2cb3d250295f:/# etcdctl put hello world10
{"level":"warn","ts":"2023-01-14T03:30:09.523Z","logger":"etcd-client","caller":"v3/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc000234000/172.20.0.3:2379","attempt":0,"error":"rpc error: code = Unknown desc = malformed header: missing HTTP content-type"}
Error: rpc error: code = Unknown desc = malformed header: missing HTTP content-type
root@2cb3d250295f:/# etcdctl put hello world11
{"level":"warn","ts":"2023-01-14T03:38:58.177Z","logger":"etcd-client","caller":"v3/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc000452a80/172.20.0.3:2379","attempt":0,"error":"rpc error: code = DeadlineExceeded desc = context deadline exceeded"}
Error: context deadline exceeded
root@2cb3d250295f:/# etcdctl put hello world11
{"level":"warn","ts":"2023-01-14T03:39:05.726Z","logger":"etcd-client","caller":"v3/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc000234000/172.20.0.3:2379","attempt":0,"error":"rpc error: code = DeadlineExceeded desc = context deadline exceeded"}
Error: context deadline exceeded
root@2cb3d250295f:/# etcdctl put hello world12
{"level":"warn","ts":"2023-01-14T03:40:00.185Z","logger":"etcd-client","caller":"v3/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc00024e000/172.20.0.3:2379","attempt":0,"error":"rpc error: code = DeadlineExceeded desc = context deadline exceeded"}
Error: context deadline exceeded
root@2cb3d250295f:/# etcdctl put hello1 world1
OK
root@2cb3d250295f:/# etcdctl put hello1 world2
{"level":"warn","ts":"2023-01-14T03:40:22.492Z","logger":"etcd-client","caller":"v3/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc000236000/172.20.0.3:2379","attempt":0,"error":"rpc error: code = Unknown desc = malformed header: missing HTTP content-type"}
Error: rpc error: code = Unknown desc = malformed header: missing HTTP content-type

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[Phoenix500526]

The reason behind this issue is that the server cannot handle the scenario in which the client closes the watch connection.
Resolved in #105