[breaking] cli: format json always start with a json object

[alessio-perugini]

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• Tests for the changes have been added (for bug fixes / features)
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• configuration.schema.json updated if new parameters are added.

What kind of change does this PR introduce?

We're wrapping in json object all the results that previously were emitting directly an array

What is the current behavior?

Currently, some commands when printing with json, are starting with an array instead of an object

What is the new behavior?

We uniformed every command to always output a json Object.

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

Other information

[codecov]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (ae24226) 67.23% compared to head (72a06b4) 67.16%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2407      +/-   ##
==========================================
- Coverage   67.23%   67.16%   -0.07%     
==========================================
  Files         210      210              
  Lines       20519    20523       +4     
==========================================
- Hits        13796    13785      -11     
- Misses       5589     5600      +11     
- Partials     1134     1138       +4     

Flag	Coverage Δ
unit	67.16% <77.27%> (-0.07%)	⬇️

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

Files	Coverage Δ
internal/cli/board/listall.go	57.44% <100.00%> (ø)
internal/cli/config/add.go	93.61% <100.00%> (ø)
internal/cli/config/set.go	85.36% <100.00%> (ø)
internal/cli/core/list.go	90.62% <100.00%> (ø)
internal/cli/lib/check_deps.go	76.81% <100.00%> (ø)
internal/cli/lib/examples.go	55.88% <100.00%> (ø)
internal/cli/lib/list.go	94.44% <100.00%> (ø)
internal/cli/config/dump.go	71.42% <50.00%> (ø)
internal/cli/core/search.go	74.75% <80.00%> (ø)
internal/cli/board/list.go	34.43% <60.00%> (ø)
... and 2 more

... and 2 files with indirect coverage changes

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[cmaglie]