Refactored config to not use viper singleton instance

[silvanocerza]

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• The PR has no duplicates (please search among the Pull Requests
  before creating one)
• The PR follows
  our contributing guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce?
  Refactors how the configs are initialized and fixes config init.

• What is the current behavior?
  Configs are managed using the viper package singleton, config init command reads from existing settings when initializing a new config file.

• What is the new behavior?
  Configs are not managed anymore with the viper package singleton but using a global variable internal to the configuration package of the arduino-cli.
  The config init command now initializes new config files using the default values without reading from existing files.

• Does this PR introduce a breaking change?
  Yes.

• Other information:
  None.

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[ubidefeo]

Tested and it finally works

[cmaglie]

I've added some more commits, so I approve all the rest :-)
@silvanocerza if you are ok with my changes, IMHO this is ready to merge.