Add enable-ws flag in server command

[DarianShawn]

Description

The WebSocket enpoint was enabled by default, it would consumes too many connections of the RPC node when exposed in the Internet.

This PR adds the enable-ws flag to the server command, and disable the WebSocket endpoint by default.

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually

Manual tests

• setup a new dev mode server, using enable-ws flag or without it.
• Use WebSocket client, connect to localhost WebSocket endpoint.

We should not be able to connect to ws://localhost:8545/ws endpoint when enable-ws flag not set. And vice versa.

Documentation update

Would update the documentation when new released done.

[codecov-commenter]

Codecov Report

Merging #152 (5dc5810) into dev (dae96a0) will decrease coverage by 0.00%.
The diff coverage is 25.00%.

@@            Coverage Diff             @@
##              dev     #152      +/-   ##
==========================================
- Coverage   51.63%   51.63%   -0.01%     
==========================================
  Files         112      112              
  Lines       16586    16588       +2     
==========================================
+ Hits         8565     8566       +1     
  Misses       7287     7287              
- Partials      734      735       +1     

Impacted Files	Coverage Δ
jsonrpc/jsonrpc.go	16.94% <25.00%> (-0.77%)	⬇️
protocol/syncer.go	66.80% <0.00%> (+0.41%)	⬆️

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[abrahamcruise321]

ok.