Renamed FQBN.Packager -> FQBN.Vendor

[cmaglie]

Please check if the PR fulfills these requirements

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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)
• 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?

Just an API change, before publishing a package.

What is the current behavior?

What is the new behavior?

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

No, because the package is not yet published.

Other information

[codecov]

Codecov Report

Attention: Patch coverage is 63.63636% with 4 lines in your changes missing coverage. Please review.

Project coverage is 67.77%. Comparing base (0847849) to head (37b971c).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
commands/service_upload.go	0.00%	2 Missing ⚠️
internal/cli/board/list.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2836      +/-   ##
==========================================
- Coverage   67.81%   67.77%   -0.05%     
==========================================
  Files         238      238              
  Lines       22402    22402              
==========================================
- Hits        15193    15184       -9     
- Misses       6020     6027       +7     
- Partials     1189     1191       +2     

Flag	Coverage Δ
unit	67.77% <63.63%> (-0.05%)	⬇️

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