etcdmain: add discovery-srv-name

[hexfusion]

Small update to help for discovery-srv-name feature.

ref: #8690

[codecov-io]

Codecov Report

Merging #9252 into master will increase coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #9252      +/-   ##
==========================================
+ Coverage   75.83%   75.93%   +0.09%     
==========================================
  Files         363      363              
  Lines       30194    30194              
==========================================
+ Hits        22898    22927      +29     
+ Misses       5688     5671      -17     
+ Partials     1608     1596      -12

Impacted Files	Coverage Δ
clientv3/namespace/watch.go	87.87% <0%> (-12.13%)	⬇️
proxy/grpcproxy/register.go	69.44% <0%> (-11.12%)	⬇️
client/members.go	81.45% <0%> (-4.04%)	⬇️
pkg/netutil/netutil.go	66.66% <0%> (-2.09%)	⬇️
internal/mvcc/watchable_store.go	86.71% <0%> (-0.74%)	⬇️
clientv3/watch.go	94.6% <0%> (-0.5%)	⬇️
raft/raft.go	91.68% <0%> (-0.28%)	⬇️
etcdserver/server.go	79.29% <0%> (-0.23%)	⬇️
embed/config.go	59.85% <0%> (ø)	⬆️
etcdserver/v3_server.go	82.17% <0%> (+0.25%)	⬆️
... and 14 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 42ef97d...c2171f9. Read the comment docs.

[gyuho]

lgtm. thanks!