[BREAKING] gRPC / golang Configuration API refactoring

[cmaglie]

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• The PR has no duplicates (please search among the Pull Requests
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• The PR follows
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• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• UPGRADING.md has been updated with a migration guide (for breaking changes)
• configuration.schema.json updated if new parameters are added.

What kind of change does this PR introduce?

This PR introduces a big change in the configuration API, the main goals for this PR are:

• Making the gRPC API more prominent even in the internal of the golang code, in this case, after merging the PR, the command line interface implementation becomes 100% dependent on the gRPC API, (no more bypass)
• The configuration API (hopefully) becomes more flexible than it was before, allowing a more granular control of the written fields
• Makes real the 'third pillar' of the Arduino CLI (using the code by importing in another golang project).

What is the current behavior?

There should be very few changes in the CLI behavior, in theory, final users should not notice any change.

What is the new behavior?

Does this PR introduce a breaking change, and is titled accordingly?

Yes, the gRPC Settings* API changed a lot, adaption on the client is required.

Other information

[codecov]

Codecov Report

Attention: Patch coverage is 74.24299% with 689 lines in your changes are missing coverage. Please review.

Project coverage is 70.13%. Comparing base (03d8653) to head (cec1fdb).
Report is 4 commits behind head on master.

Files	Patch %	Lines
internal/go-configmap/types.go	46.52%	69 Missing and 8 partials ⚠️
commands/service_monitor.go	62.69%	53 Missing and 19 partials ⚠️
commands/service_settings.go	69.51%	39 Missing and 11 partials ⚠️
commands/cmderrors/cmderrors.go	14.89%	40 Missing ⚠️
commands/instances.go	72.91%	30 Missing and 9 partials ⚠️
commands/service_upload_burnbootloader.go	0.00%	35 Missing ⚠️
commands/service_upload.go	54.41%	29 Missing and 2 partials ⚠️
commands/service_compile.go	66.66%	24 Missing and 4 partials ⚠️
internal/go-configmap/cli.go	65.07%	16 Missing and 6 partials ⚠️
internal/cli/config/init.go	64.40%	12 Missing and 9 partials ⚠️
... and 50 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2565      +/-   ##
==========================================
+ Coverage   69.51%   70.13%   +0.61%     
==========================================
  Files         207      222      +15     
  Lines       20285    21124     +839     
==========================================
+ Hits        14102    14816     +714     
- Misses       5069     5132      +63     
- Partials     1114     1176      +62     

Flag	Coverage Δ
unit	70.13% <74.24%> (+0.61%)	⬆️

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[alessio-perugini]

LGTM

I'd say after the PR that unifies the usage of oneOf in our API, we can schedule a round of manual testing to catch any regression (if any) not seen by our integration tests.

[umbynos]

Overall LGTM, I did not find any major problem.
Should we update also this: https://github.com/arduino/arduino-cli/blob/master/docs/integration-options.md ?

[cmaglie]

Should we update also this: https://github.com/arduino/arduino-cli/blob/master/docs/integration-options.md?

Yes, BTW I'm doing it in another branch as part of a general revamp of the documentation.