feat: update header detection logic

[carlbrugger]

This PR introduces new header detection options.

Guide: FlatFilers/Guides#962

Usage:

// default
listener.use(
  ExcelExtractor()
)
// or...
listener.use(
  ExcelExtractor({
    headerDetectionOptions: {
      algorithm: 'default',
      rowsToSearch: 30, // Default is 10
    },
  })
)

// explicitHeaders
listener.use(
  ExcelExtractor({
    headerDetectionOptions: {
      algorithm: 'explicitHeaders',
      headers: ['fiRsT NamE', 'LaSt nAme', 'emAil'],
    },
  })
)

// specificRows
listener.use(
  ExcelExtractor({
    headerDetectionOptions: {
      algorithm: 'specificRows',
      rowNumbers: [2], // 0 based
    },
  })
)

[bangarang]

Looks like a bunch of the getHeaders logic is shared - wonder if we abstract out just the logical changes that are different here instead of just the return Promise?