Add support to use existing database snapshot

[nagdahimanshu]

What was the problem?

This PR resolves #191

How was it solved?

• Add flag network, snapshot-path, snapshot-url
  • Any one of these (snapshot-path, snapshot-url) is required with network
• Skip all node validation when snapshot-path or snapshot-url is passed
• Use DB snapshot directly to create snapshot block
• Add support to download, validate and extract snapshot in case of snapshot-url flag
• Add support to extract snapshot when snapshot is .taz.gz
• Migrator is able to create snapshot block
• Lisk Core v4 node should start
• Update docs
• Add unit tests

How was it tested?

Locally against mainnet

• ./bin/run -s SNAPSHOT_HEIGHT --snapshot-path SNAPSHOT_PATH (either extracted path or path ends with .tar.gz) --network NETWORK
• ./bin/run -s SNAPSHOT_HEIGHT --snapshot-url SNAPSHOT_URL (url starts with http/https and ends with .tar.gz) --network NETWORK
• ./bin/run -s SNAPSHOT_HEIGHT --auto-start-lisk-core-v4

[codecov]

Codecov Report

Merging #193 (1204b11) into release/2.0.0 (566854f) will increase coverage by 0.85%.
The diff coverage is 98.07%.

@@                Coverage Diff                @@
##           release/2.0.0     #193      +/-   ##
=================================================
+ Coverage          81.23%   82.08%   +0.85%     
=================================================
  Files                 24       25       +1     
  Lines                778      815      +37     
  Branches             111      117       +6     
=================================================
+ Hits                 632      669      +37     
  Misses               146      146              

Files	Coverage Δ
src/assets/pos.ts	90.14% <ø> (-1.43%)	⬇️
src/utils/block.ts	53.19% <100.00%> (+9.60%)	⬆️
src/utils/fs.ts	100.00% <100.00%> (ø)
src/utils/network.ts	92.59% <100.00%> (+9.25%)	⬆️
src/utils/number.ts	100.00% <100.00%> (ø)
src/utils/path.ts	100.00% <100.00%> (ø)
src/utils/node.ts	43.96% <0.00%> (ø)