fix: better error message for bad retrieval URL

[alanshaw]

Hopefully to shed some light on error message @fforbeck is experiencing:

bafybeia46acqnqszcpzi3yczdg6kt6fpeloxosau4totgufl5u4p2ocjyi:
  NetworkError
    status: 500
    message: processing query: no {blob} or {blobCID} endpoint found in 1 addresses

• Adds the addresses considered to the error message
• Adds the CID of index we're attempting to retrieve to the error message

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/service/service.go	66.66%	1 Missing ⚠️

Files with missing lines	Coverage Δ
pkg/service/service.go	79.35% <66.66%> (+0.04%)	⬆️

... and 1 file with indirect coverage changes

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