Updateable reserveRatio for GNS

[jona]

Summary

We currently have no way to set reserveRatio in the GNS contract through governance.

Solution

Add a setReserveRatio function that allows us to set reserverRatio

[codecov]

Codecov Report

Merging #515 (f8503f0) into dev (6962037) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev     #515      +/-   ##
==========================================
+ Coverage   91.91%   91.96%   +0.04%     
==========================================
  Files          33       33              
  Lines        1658     1667       +9     
  Branches      282      284       +2     
==========================================
+ Hits         1524     1533       +9     
  Misses        134      134              

Flag	Coverage Δ
unittests	91.96% <100.00%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
contracts/discovery/GNS.sol	99.30% <100.00%> (+0.04%)	⬆️

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[abarmat]

I've left some comments

[abarmat]

gns.nameSignals(me.address, 0) returns an object that lets you access attributes by both position and key:

[
  BigNumber { _hex: '0x858ffc3f497c9112', _isBigNumber: true },
  BigNumber { _hex: '0x874391d0dd1fdf42', _isBigNumber: true },
  '0x71a94176484d9e0d2ff853a92e162a0493fafa1823a0841400c054769bd895a1',
  10,
  false,
  BigNumber { _hex: '0x00', _isBigNumber: true },
  vSignal: BigNumber { _hex: '0x858ffc3f497c9112', _isBigNumber: true },
  nSignal: BigNumber { _hex: '0x874391d0dd1fdf42', _isBigNumber: true },
  subgraphDeploymentID: '0x71a94176484d9e0d2ff853a92e162a0493fafa1823a0841400c054769bd895a1',
  reserveRatio: 10,
  disabled: false,
  withdrawableGRT: BigNumber { _hex: '0x00', _isBigNumber: true }
]

You should be able to do something like:
expect(pool.reserveRatio).eq(value)

[jona]

I was following the pattern used here: https://github.com/graphprotocol/contracts/blob/dev/test/gns.test.ts#L157-L159

Wanted to make sure to edit and mutate as little as possible with this PR

[abarmat]

I understand. I moved away from using positional arguments on a refactor I did for this PR #497

We can use the old pattern here and then eventually when audit passes on #497 and if governance decides to move forward with that upgrade we can rebase/merge.