Decouple Debug logging from fail_on_error logic

[AndyHunt66]

When using the rename, copy_fields or truncate_fields processors, and specifying multiple fields to be processed

if the processor fails on one of the fields (usually because a field is not present), a Debug log message will only be thrown if fail_on_error is true .
Logging of the error should be independent of the fail_on_error flag.

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Ref #12451

[ruflin]

LGTM

@kvch Could you also have a look?

[ruflin]

jenkins, test this

[kvch]

Thank you!

[ruflin]

jenkins, test this

[kvch]

Failing tests are unrelated.