vendor: update "grpc-gateway" to v1.4.1

[hexfusion]

This was cut last night and I would like to keep on lastest if possible. grpc-ecosystem/grpc-gateway#658 which was added to this release will allow us to consolidate our 3 swagger JSON specs into 1. I think this will be much more user-friendly for folks looking to use the spec to generate code.

[codecov-io]

Codecov Report

Merging #9757 into master will increase coverage by 1.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #9757      +/-   ##
==========================================
+ Coverage   68.64%   69.67%   +1.03%     
==========================================
  Files         374      375       +1     
  Lines       35129    35179      +50     
==========================================
+ Hits        24114    24512     +398     
+ Misses       9242     8911     -331     
+ Partials     1773     1756      -17

Impacted Files	Coverage Δ
proxy/grpcproxy/register.go	69.44% <0%> (-13.89%)	⬇️
etcdctl/ctlv3/command/printer_simple.go	72.48% <0%> (-1.35%)	⬇️
clientv3/balancer/grpc1.7-health.go	85.17% <0%> (-1.17%)	⬇️
etcdserver/v3_server.go	75.11% <0%> (-0.96%)	⬇️
etcdserver/api/rafthttp/stream.go	78.96% <0%> (-0.86%)	⬇️
raft/raft.go	90.99% <0%> (-0.7%)	⬇️
pkg/proxy/server.go	60.2% <0%> (-0.68%)	⬇️
mvcc/watchable_store.go	82.74% <0%> (-0.36%)	⬇️
etcdserver/api/v3rpc/watch.go	77.44% <0%> (-0.34%)	⬇️
integration/cluster_proxy.go	100% <0%> (ø)
... and 34 more

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[gyuho]

lgtm thanks!