feat(flashcache): flash cache in cluster

[sejust]

Fixes: #2943

Main Issue: #2943

Motivation

Sharding cache in distributed memories of cluster servers.

Modifications

• flash server: distributed memory cache of one server.
• flash group: cache group stored in master raft.
• cli: command tools of flash node and flash group.

Types of changes

• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Bugfix (non-breaking change which fixes an issue)
• Documentation Update (if none of the other choices apply)
• So on...

Verifying this change

• Make sure that the change passes the testing checks.

This change is already covered by existing tests.

Does this pull request potentially affect one of the following parts:

• Master
• MetaNode
• DataNode
• ObjectNode
• AuthNode
• FlashNode
• Blobstore
• Client
• Cli
• SDK
• Other Tools
• Common Packages
• Dependencies
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Review Expection

• in-two-days
• weekly
• free-time
• whenever

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[codecov]

Codecov Report

Attention: Patch coverage is 40.19720% with 2608 lines in your changes are missing coverage. Please review.

Project coverage is 40.56%. Comparing base (bdffd66) to head (9567c44).
Report is 58 commits behind head on master.

❗ Current head 9567c44 differs from pull request most recent head 3a2f5da

Please upload reports for the commit 3a2f5da to get more accurate results.

Files	Patch %	Lines
proto/distributed_cache.pb.go	1.25%	1098 Missing ⚠️
cli/cmd/flashgroup.go	0.00%	356 Missing ⚠️
proto/distributed_cache.go	0.00%	158 Missing ⚠️
flashnode/cachengine/engine.go	38.16%	119 Missing and 9 partials ⚠️
cli/cmd/flashnode.go	8.39%	120 Missing ⚠️
master/flash_group.go	74.31%	84 Missing and 28 partials ⚠️
flashnode/cachengine/block.go	46.44%	93 Missing and 5 partials ⚠️
master/flash_node_topology.go	73.60%	52 Missing and 19 partials ⚠️
cli/cmd/vol.go	0.00%	61 Missing ⚠️
master/flash_node.go	79.10%	43 Missing and 18 partials ⚠️
... and 22 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2944      +/-   ##
==========================================
+ Coverage   40.49%   40.56%   +0.07%     
==========================================
  Files         603      620      +17     
  Lines      125057   129370    +4313     
==========================================
+ Hits        50643    52485    +1842     
- Misses      70051    72412    +2361     
- Partials     4363     4473     +110     

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