Fix entry duplication at beginning of file(s)

[jsirianni]

Description of Changes

Backporting a data duplication fix that was recently released in the OTEL repo. I don't have a great understanding of the complex file input operator, but I do know that the test being added (TestIgnoreEmptyFiles) is flaky (fails most of the time) until the actual fix is implemented. Once the fix is in place, the new test passes 100% of the time for me.

while :
do
go clean -testcache ./... && go test -run TestIgnoreEmptyFiles ./operator/builtin/input/file
done

For more context around the issue:

• OTEL Issue: data duplication at the beginning of log file open-telemetry/opentelemetry-log-collection#391
• OTEL PR: fix iteration open-telemetry/opentelemetry-log-collection#413

Please check that the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• Add a changelog entry (for non-trivial bug fixes / features)
• CI passes

[codecov]

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@@           Coverage Diff           @@
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  Files           ?      133           
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  Branches        ?        0           
=======================================
  Hits            ?     7564           
  Misses          ?     2060           
  Partials        ?      465           

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[rockb1017]

FYI, on the open telemetry log collection repo, it is not flaky.

 ~/go/src/github.com/rockb1017/opentelemetry-log-collection [main|⚑ 2] 
14:31 $ while :; do go clean -testcache ./... && go test -run TestIgnoreEmptyFiles ./operator/input/file; done

ok      github.com/open-telemetry/opentelemetry-log-collection/operator/input/file      6.787s
ok      github.com/open-telemetry/opentelemetry-log-collection/operator/input/file      6.197s
ok      github.com/open-telemetry/opentelemetry-log-collection/operator/input/file      6.222s
ok      github.com/open-telemetry/opentelemetry-log-collection/operator/input/file      6.196s
ok      github.com/open-telemetry/opentelemetry-log-collection/operator/input/file      6.218s
ok      github.com/open-telemetry/opentelemetry-log-collection/operator/input/file      6.232s
ok      github.com/open-telemetry/opentelemetry-log-collection/operator/input/file      6.214s
ok      github.com/open-telemetry/opentelemetry-log-collection/operator/input/file      6.184s
ok      github.com/open-telemetry/opentelemetry-log-collection/operator/input/file      6.245s
ok      github.com/open-telemetry/opentelemetry-log-collection/operator/input/file      6.173s
ok      github.com/open-telemetry/opentelemetry-log-collection/operator/input/file      6.193s
ok      github.com/open-telemetry/opentelemetry-log-collection/operator/input/file      6.207s

[cpheps]

LGTM, Please update branch