engine: Add fee synchronisation management [POC]

[shazbert]

Dear happy peoples,

PR Description

• Adds fee management routine [poc] that will synchronise fees every hour for authenticated enabled exchanges.
• This will also start to synchronise tradable pairs every hour.

NOTEs:

• So this reduces the need to send a HTTP request every time a fee is needed
• Also I have opted to store as rate to minimize the division operation, but it's not really a big improvement on speed. So if you don't like it 🤷

Requires #1370

Kind Regards,

Type of change

Please delete options that are not relevant and add an x in [] as item is complete.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How has this been tested

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration and also consider improving test coverage whilst working on a certain feature or package.

• [ ] go test ./... -race
• [ ] golangci-lint run
• [ ] Test X

Checklist

• [ ] My code follows the style guidelines of this project
• [ ] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation and regenerated documentation via the documentation tool
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally and on Github Actions/AppVeyor with my changes
• [ ] Any dependent changes have been merged and published in downstream modules

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 64.81481% with 38 lines in your changes are missing coverage. Please review.

Project coverage is 37.77%. Comparing base (1e95ae9) to head (a03d49f). Report is 1 commits behind head on master.

:exclamation: Current head a03d49f differs from pull request most recent head b859808. Consider uploading reports for the commit b859808 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1376      +/-   ##
==========================================
- Coverage   37.91%   37.77%   -0.15%     
==========================================
  Files         411      413       +2     
  Lines      147198   147904     +706     
==========================================
+ Hits        55817    55869      +52     
- Misses      83588    84254     +666     
+ Partials     7793     7781      -12     

Files	Coverage Δ
config/config.go	87.91% <100.00%> (+0.33%)	:arrow_up:
exchanges/exchange.go	80.64% <100.00%> (+1.19%)	:arrow_up:
exchanges/fee/fee.go	100.00% <100.00%> (ø)
engine/engine.go	41.82% <60.00%> (+0.15%)	:arrow_up:
engine/fee_management.go	58.33% <58.33%> (ø)
exchanges/kucoin/kucoin_wrapper.go	37.19% <18.75%> (+0.10%)	:arrow_up:

... and 72 files with indirect coverage changes