[breaking] gRPC UpdateIndex and UpdateLibrariesIndex improvements

[cmaglie]

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• The PR has no duplicates (please search among the Pull Requests
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• 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?

UpdateIndex and UpdateLibrariesIndex now have the update_if_older_than_secs field that prevents updating the index if it has already been updated. Also, the response is more explicit with oneof(..) clause, and the status of each update (in case of multiple index updates) is returned in the response.

The JSON output has been implemented for commands core update-index and lib update-index.

What is the current behavior?

$ arduino-cli lib update-index --format json
$ arduino-cli core update-index --additional-urls=file:///home/cmaglie/Workspace/arduino-cli/internal/integrationtest/testdata/test_index.json  --format json
$

What is the new behavior?

$ arduino-cli lib update-index --format json
{
  "libraries_index": {
    "index_url": "https://downloads.arduino.cc/libraries/library_index.tar.bz2",
    "status": "updated"
  }
}
$ arduino-cli core update-index --additional-urls=file:///home/cmaglie/Workspace/arduino-cli/internal/integrationtest/testdata/test_index.json  --format json
{
  "updated_indexes": [
    {
      "index_url": "https://downloads.arduino.cc/packages/package_index.tar.bz2",
      "status": "updated"
    },
    {
      "index_url": "file:///home/megabug/Workspace/arduino-cli/internal/integrationtest/testdata/test_index.json",
      "status": "skipped"
    }
  ]
}
$

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

Yes

Other information

[codecov]

Codecov Report

Attention: Patch coverage is 74.66667% with 38 lines in your changes are missing coverage. Please review.

Project coverage is 69.58%. Comparing base (31e3288) to head (e92a812).
Report is 1 commits behind head on master.

Files	Patch %	Lines
commands/instances.go	73.77%	14 Missing and 2 partials ⚠️
commands/daemon/daemon.go	50.00%	11 Missing ⚠️
internal/cli/lib/search.go	55.55%	2 Missing and 2 partials ⚠️
internal/cli/core/search.go	75.00%	2 Missing and 1 partial ⚠️
internal/cli/feedback/result/rpc.go	92.59%	2 Missing ⚠️
internal/cli/lib/update_index.go	77.77%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2569      +/-   ##
==========================================
+ Coverage   69.48%   69.58%   +0.09%     
==========================================
  Files         205      205              
  Lines       20204    20267      +63     
==========================================
+ Hits        14038    14102      +64     
- Misses       5045     5049       +4     
+ Partials     1121     1116       -5     

Flag	Coverage Δ
unit	69.58% <74.66%> (+0.09%)	⬆️

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[alessio-perugini]

Looks good, in the future we could expand the daemon and cli --json tests, checking that IndexUpdateReport contains what we'd expect.

[cmaglie]

Related to #2565