Monitor avg gas price

[stronk-dev]

What does this pull request do? Explain your changes. (required) Removes the hardcoded avg gas price, rather track an actual moving average in the GasPriceMonitor

Specific updates (required)

• Remove hardcoded default
• Calculate moving average over gas price samples to expose an average gas price
• Pass actual avg gas price in FaceValue function

How did you test each of these updates (required) Not yet

Does this pull request close any open issues? Related to #3746 and #3744

Checklist:

• [ ] Read the contribution guide
• [ ] make runs successfully
• [ ] All tests in ./test.sh pass
• [ ] README and other documentation updated
• [ ] Pending changelog updated

[stronk-dev]

this seemed like a reasonably simple avg gas price calculation: each new sample contributes 20% weight, the previous rolling value keeps 80%. of course we could also keep a set of samples or change these weights (or make them configurable, but this feels like something that should just have sane defaults and no-one should really want to touch)

[codecov[bot]]

Codecov Report

:x: Patch coverage is 82.92683% with 7 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 31.97435%. Comparing base (d8e520a) to head (9a0e4c4). :warning: Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
eth/gaspricemonitor.go	88.57143%	3 Missing and 1 partial :warning:
pm/stub.go	40.00000%	2 Missing and 1 partial :warning:

Additional details and impacted files

@@                 Coverage Diff                 @@
##              master       #3752         +/-   ##
===================================================
+ Coverage   31.94444%   31.97435%   +0.02991%     
===================================================
  Files            158         158                 
  Lines          47520       47560         +40     
===================================================
+ Hits           15180       15207         +27     
- Misses         31437       31447         +10     
- Partials         903         906          +3     

Files with missing lines	Coverage Δ
pm/recipient.go	88.46154% <100.00000%> (+0.04952%)	:arrow_up:
pm/stub.go	56.25000% <40.00000%> (-0.30431%)	:arrow_down:
eth/gaspricemonitor.go	85.81081% <88.57143%> (+0.72309%)	:arrow_up:

... and 3 files with indirect coverage changes

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Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update d8e520a...9a0e4c4. Read the comment docs.

Files with missing lines	Coverage Δ
pm/recipient.go	88.46154% <100.00000%> (+0.04952%)	:arrow_up:
pm/stub.go	56.25000% <40.00000%> (-0.30431%)	:arrow_down:
eth/gaspricemonitor.go	85.81081% <88.57143%> (+0.72309%)	:arrow_up:

... and 3 files with indirect coverage changes

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