feat: add sync status rpc interface

[wenchaopeng]

Signed-off-by: wenchao 659672152@qq.com

Proposed changes in this pull request

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Type

• Bug fix: (Link to the issue #{issue No.})
• Feature (Non-breaking change)
• Feature (Breaking change)
• Documentation Improvement

Checklist

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• Read the CONTRIBUTION.
• All the tests are passing after the introduction of new changes.
• Added tests respective to the part of code I have written.
• Added proper documentation where ever applicable.
• Code has been written according to Golang-Style-Guide

Extra information

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[codecov]

Codecov Report

Merging #377 into master will decrease coverage by 0.19%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master     #377     +/-   ##
=========================================
- Coverage   44.73%   44.53%   -0.2%     
=========================================
  Files         168      168             
  Lines       17167    17209     +42     
=========================================
- Hits         7679     7664     -15     
- Misses       8297     8358     +61     
+ Partials     1191     1187      -4

Impacted Files	Coverage Δ
rpc/api/net.go	0% <0%> (ø)	⬆️
p2p/sync.go	8.06% <0%> (-0.07%)	⬇️
p2p/messageMonitor.go	45.94% <0%> (-11.12%)	⬇️
p2p/types.go	58.62% <0%> (-6.9%)	⬇️
common/sync/hashmap/hashmap.go	95.81% <0%> (+0.93%)	⬆️
rpc/api/rewards.go	55.43% <0%> (+3.14%)	⬆️

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[gythialy]

please make sure that syncingTime is thread safe