refactor(storagenode): add LogStreamReplicaMetadata to /varlog.snpb.LogIO to replace LogStreamMetadata

[ijsong]

What this PR does

Add /varlog.snpb.LogIO/LogStreamReplicaMetadata to replace
/varlog.snpb.LogIO/LogStreamMetadata. The LogStreamMetadata returns
proto/varlogpb/LogStreamDescriptor that have deprecated fields Head and
Tail. Instead, the LogStreamReplicaMetadata returns
proto/snpb/LogStreamReplicaMetadataDescriptor that is proper to the intend of
RPC.

Which issue(s) this PR resolves

Ref: #73

Anything else

---

This change is 

[codecov-commenter]

Codecov Report

Merging #140 (926348d) into main (c4d0c8d) will decrease coverage by 0.24%.
The diff coverage is 41.53%.

@@            Coverage Diff             @@
##             main     #140      +/-   ##
==========================================
- Coverage   62.83%   62.59%   -0.25%     
==========================================
  Files         125      125              
  Lines       16883    16996     +113     
==========================================
+ Hits        10609    10638      +29     
- Misses       5727     5804      +77     
- Partials      547      554       +7     

Impacted Files	Coverage Δ
internal/storagenode/client/log_client.go	45.37% <0.00%> (-3.72%)	⬇️
internal/storagenode/log_server.go	41.05% <0.00%> (-4.83%)	⬇️
pkg/varlog/log.go	0.00% <0.00%> (ø)
pkg/varlog/operations.go	0.00% <0.00%> (ø)
proto/snpb/metadata.go	0.00% <0.00%> (ø)
pkg/varlogtest/log.go	71.46% <70.58%> (-0.15%)	⬇️
pkg/varlogtest/admin.go	42.03% <85.71%> (+0.61%)	⬆️
internal/storagenode/logstream/executor.go	75.94% <0.00%> (-1.90%)	⬇️
internal/storagenode/logstream/committer.go	81.85% <0.00%> (-1.07%)	⬇️
internal/metarepos/report_collector.go	77.86% <0.00%> (-0.81%)	⬇️
... and 1 more

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