Update 3.4 changelog to prepare for the release of 3.4.19

[ahrtr]

Signed-off-by: Benjamin Wang wachao@vmware.com

Refer to #14105

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[codecov-commenter]

Codecov Report

Merging #14202 (1914e42) into main (186c895) will decrease coverage by 0.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main   #14202      +/-   ##
==========================================
- Coverage   75.36%   75.24%   -0.12%     
==========================================
  Files         455      455              
  Lines       36859    36859              
==========================================
- Hits        27778    27735      -43     
- Misses       7340     7380      +40     
- Partials     1741     1744       +3     

Flag	Coverage Δ
all	75.24% <ø> (-0.12%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
client/v3/leasing/cache.go	87.77% <0.00%> (-3.89%)	⬇️
client/pkg/v3/testutil/recorder.go	76.27% <0.00%> (-3.39%)	⬇️
server/etcdserver/api/v3rpc/member.go	93.54% <0.00%> (-3.23%)	⬇️
server/etcdserver/cluster_util.go	70.35% <0.00%> (-3.17%)	⬇️
server/proxy/grpcproxy/watch.go	93.64% <0.00%> (-2.90%)	⬇️
client/pkg/v3/transport/listener.go	57.18% <0.00%> (-2.40%)	⬇️
server/etcdserver/api/v3rpc/watch.go	85.57% <0.00%> (-2.35%)	⬇️
server/etcdserver/api/rafthttp/peer.go	85.06% <0.00%> (-1.95%)	⬇️
server/auth/store.go	84.13% <0.00%> (-1.16%)	⬇️
server/storage/mvcc/kvstore_txn.go	78.02% <0.00%> (-1.10%)	⬇️
... and 15 more

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[ahrtr]

cc @serathius @spzala @ptabor