tail: ensure db file is unique

[patrick-stephens]

If you do not have a unique db file across multiple tail inputs then you may get inconsistent behaviour, e.g. https://fluent-all.slack.com/archives/C0CTQGHKJ/p1758561924366279?thread_ts=1758224398.125199&cid=C0CTQGHKJ

[patrick-stephens]

I take issue with requiring contractions - any reason for it @alexakreizinger ?

  Warning: [vale] reported by reviewdog 🐶
  [FluentBit.Contractions] Feel free to use 'it's' instead of 'it is'.
  
  Raw Output:
  {"message": "[FluentBit.Contractions] Feel free to use 'it's' instead of 'it is'.", "location": {"path": "pipeline/inputs/tail.md", "range": {"start": {"line": 78, "column": 56}}}, "severity": "INFO"}
  reviewdog: found at least one result in diff
Error: Vale and reviewdog exited with status code: 1

[alexakreizinger]

@patrick-stephens not required, just suggested, so feel free to take or ignore the suggestion as you see fit :) although instead of warning there is a suggestion-level vale message we could implement instead—what do you think @esmerel?

[alexakreizinger]

actually, looking more closely at the linter message: I think the "warning" part is just a generic message from reviewdog, because in the raw output I see "severity": "INFO". so we might not be able to change the linter message itself, but regardless, no pressure to use contractions unless you want to.