Normalize log/error capitalization

[antgamdia]

Describe the bug
The log traces and the error messages have an inconsistent capitalization across the codebase.

To Reproduce
N/A

Expected behavior
According to https://google.github.io/styleguide/go/decisions.html#error-strings, user-faced traces (like logs) should be uppercased whereas the errors (like errors.new or fmt.errorf) should be lowercased.

Screenshots
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Desktop (please complete the following information):

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Additional context

Originally posted by @absoludity in #6647 (comment)