NNS1-3480: Refactors generateCsvFileToSave to manage datasets for more complex CSV files

[yhabib]

Motivation

The report functionality for transactions requires more complex .csv structures, as shown in the screenshot. To achieve this, we need to introduce the concept of datasets, which are small tables within the file. All datasets will share the same headers.

Changes

• Refactors generateCsvFileToSave to handle datasets across multiple levels.
• Introduces a new function, combineDatasetsToCsv, to merge multiple datasets into one.
• Updates ExportNeuronsButton, the existing consumer of generateCsvFileToSave, to supply a dataset.

Tests

• Added new tests for the updated API.
• Refactored existing tests for the new API.

Todos

• Add entry to changelog (if necessary).
  Not necessary