Provide meta file options for environmentAliases and environmentTypeNames

[joelgallant]

Closes #20.

I'm not entirely happy with the name environmentSourceNames, but environmentVariableName is already used for 'APP_CONFIG'.

[cypress]

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Test summary

9 • 0 • 0 • 0

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Run details

Project	App Config
Status	Passed
Commit	17d1894
Started	Jan 27, 2021 5:42 PM
Ended	Jan 27, 2021 5:44 PM
Duration	01:33 💡
OS	Linux Ubuntu - 18.04
Browser	Electron 87

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[codecov-io]

Codecov Report

Merging #98 (17d1894) into master (a829ade) will increase coverage by 0.03%.
The diff coverage is 97.14%.

@@            Coverage Diff             @@
##           master      #98      +/-   ##
==========================================
+ Coverage   89.03%   89.06%   +0.03%     
==========================================
  Files          21       21              
  Lines        1724     1738      +14     
  Branches      407      414       +7     
==========================================
+ Hits         1535     1548      +13     
- Misses        189      190       +1     

Impacted Files	Coverage Δ
app-config/src/environment.ts	92.85% <90.90%> (-7.15%)	⬇️
app-config/src/config-source.ts	92.13% <100.00%> (+0.08%)	⬆️
app-config/src/config.ts	96.66% <100.00%> (+0.19%)	⬆️
app-config/src/extensions.ts	90.04% <100.00%> (ø)
app-config/src/meta.ts	94.73% <100.00%> (ø)

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[gregnr]

This is awesome, thanks for implementing this so quickly!

I agree that naming this new variable is tough since we have many meanings of 'environment' in app-config. Other ideas that come to mind are something like environmentInputNames or environmentSourceNames since it describes the names of variables used for environment input/source.