feat(flashcache): flash cache in cluster

[sejust]

Fixes: #2943

Main Issue: #2943

Motivation

Sharding cache in distributed memories of cluster servers.

Modifications

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

Types of changes

• [ ] New feature (non-breaking change which adds functionality)
• [x] 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

• [x] 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:

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

Documentation

• [ ] doc
• [ ] doc-required
• [ ] doc-not-needed
• [x] doc-complete

Review Expection

• [ ] in-two-days
• [ ] weekly
• [x] free-time
• [ ] whenever

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