etcdserver: mark AuthStatus as no side effect request

[mitake]

This is a follow up change of #11536
The newly added AuthStatus() RPC doesn't have side effect against the state machine so we should mark it as no side effect request for avoiding replay overhead.

cc @tarcinil

[tarcinil]

[codecov-io]

Codecov Report

Merging #11610 into master will decrease coverage by 0.81%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #11610      +/-   ##
==========================================
- Coverage   65.22%    64.4%   -0.82%     
==========================================
  Files         403      403              
  Lines       37651    37651              
==========================================
- Hits        24558    24251     -307     
- Misses      11499    11805     +306     
- Partials     1594     1595       +1

Impacted Files	Coverage Δ
etcdserver/apply.go	77.04% <100%> (ø)	⬆️
client/client.go	44.11% <0%> (-39.87%)	⬇️
pkg/transport/timeout_conn.go	60% <0%> (-20%)	⬇️
auth/store.go	59.94% <0%> (-18.12%)	⬇️
etcdserver/api/v3rpc/util.go	51.61% <0%> (-16.13%)	⬇️
auth/simple_token.go	76.47% <0%> (-12.61%)	⬇️
clientv3/naming/grpc.go	63.15% <0%> (-12.29%)	⬇️
proxy/grpcproxy/register.go	69.44% <0%> (-11.12%)	⬇️
etcdserver/api/v3rpc/lease.go	70.45% <0%> (-4.55%)	⬇️
pkg/testutil/recorder.go	77.77% <0%> (-3.71%)	⬇️
... and 11 more

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[spzala]

LGTM

[spzala]

Thanks @mitake Straightforward changes so merging!