gRPC: added CleanDownloadCacheDirectory rpc call

[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?

• adds the gRPC CleanDownloadCacheDirectory call
• removes dependency on the configuration package from internal/cli/cache/clean.go

What is the current behavior?

No changes

What is the new behavior?

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

No

Other information

[codecov]

Codecov Report

Attention: Patch coverage is 45.45455% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 69.54%. Comparing base (67d2c57) to head (bebdcce).

Files	Patch %	Lines
commands/cache/clean.go	57.14%	2 Missing and 1 partial ⚠️
commands/daemon/daemon.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2572      +/-   ##
==========================================
- Coverage   69.56%   69.54%   -0.02%     
==========================================
  Files         205      206       +1     
  Lines       20255    20264       +9     
==========================================
+ Hits        14090    14093       +3     
- Misses       5049     5054       +5     
- Partials     1116     1117       +1     

Flag	Coverage Δ
unit	69.54% <45.45%> (-0.02%)	⬇️

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