Change path to filename

[mehuman]

As per https://grafana.com/docs/alloy/latest/reference/components/local.file/

PR Description

Updating the example to match the docs. Verified with a working example.

Which issue(s) this PR fixes

Notes to the Reviewer

PR Checklist

• CHANGELOG.md updated
• [X ] Documentation added
• Tests updated
• Config converters updated

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[clayton-cornell]

Nice catch, Thanks for putting this PR through

[clayton-cornell]

@mehuman When you have a chance, can you sign the CLA so we can finalize this PR :-)