Validate KB and backup bucket exist before a restore

[jotare]

Description

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How was this PR tested?

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.48%. Comparing base (cfe1311) to head (79541ff).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3800      +/-   ##
==========================================
+ Coverage   85.38%   85.48%   +0.10%     
==========================================
  Files         571      571              
  Lines       50466    50451      -15     
  Branches    15318    15293      -25     
==========================================
+ Hits        43090    43129      +39     
+ Misses       6746     6690      -56     
- Partials      630      632       +2     

Flag	Coverage Δ
nidx	80.97% <ø> (-0.03%)	⬇️
nucliadb	74.07% <100.00%> (+0.22%)	⬆️
nucliadb-ingest	43.87% <30.00%> (+0.01%)	⬆️
nucliadb-reader	43.69% <30.00%> (-0.03%)	⬇️
nucliadb-search	54.83% <30.00%> (-0.01%)	⬇️
nucliadb-standalone	46.03% <30.00%> (-0.01%)	⬇️
nucliadb-train	44.68% <30.00%> (-0.01%)	⬇️
nucliadb-writer	47.22% <30.00%> (+0.01%)	⬆️
nucliadb_dataset	73.40% <ø> (ø)
nucliadb_models	69.72% <ø> (ø)
nucliadb_sdk	82.28% <ø> (ø)
nucliadb_telemetry	85.67% <ø> (ø)
nucliadb_utils	80.87% <ø> (ø)

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