Add support for npm overrides

[mansona]

This PR is supposed to help with the issue that is described in emberjs/ember-render-modifiers#64

Essentially npm thinks that ranges shouldn't be satisfied if you are using pre-releases. You can overcome this if you use an overrides in npm which works in a very similar way to yarn resolutions.

The issue is that if you provide an overrides config to ember-try it will just ignore it:

{
  name: 'ember-release',
  npm: {
    devDependencies: {
      'ember-source': await getChannelURL('release'),
    },
    overrides: {
      'ember-source': '$ember-source',
    },
  },
},

This PR implements npm overrides in much the same way as yarn resolutions 👍 in fact I copy and pasted all of the resolutions tests and just changed resolutions to overrides in most cases 😂

[codecov]

Codecov Report

Merging #850 (d92f586) into master (4540780) will increase coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head d92f586 differs from pull request most recent head 7a2d4e9. Consider uploading reports for the commit 7a2d4e9 to get more accurate results

@@            Coverage Diff             @@
##           master     #850      +/-   ##
==========================================
+ Coverage   94.36%   94.37%   +0.01%     
==========================================
  Files          17       17              
  Lines         550      551       +1     
==========================================
+ Hits          519      520       +1     
  Misses         31       31              

Impacted Files	Coverage Δ
lib/dependency-manager-adapters/npm.js	98.34% <100.00%> (+0.01%)	⬆️

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[kategengler]

Thanks! Can you also add something to the readme about this feature?

[mansona]

@kategengler yes that would make a lot of sense if I did that 😂 I'm working on this live on my stream so I guess I just overlooked it 🙃

I've added them now 👍

[kategengler]

Thank you!