write_hep_timeseries_sheet: Write HEP times series sheet
In ElliottMess/rapporteur: Reports on triple billion data

export_hpop_country_summary_xls Export a country-specific for HPOP billion.

write_hep_timeseries_sheet(
  df,
  wb,
  sheet_name,
  start_row,
  start_col,
  transform_value,
  ind_df,
  ind,
  year,
  type_col,
  ind_ids,
  end_year,
  iso3
)

`df`	data frame to be written
`wb`	a `openxlsx` workbook to be edited.
`sheet_name`	character name of the sheet to update
`start_row`	integer start row of styling. Passed to `openxlsx::addStyle()`
`start_col`	integer start col of styling. Passed to `openxlsx::addStyle()`
`transform_value`	Column name of column(s) with transformed indicator values, used to calculate contributions.
`ind_df`	data frame containing information on indicators
`ind`	Column name of column with indicator names.
`year`	Column name of column with years.
`type_col`	Column name of column with type data.
`ind_ids`	Named vector of indicator codes for input indicators to the Billion. Although separate indicator codes can be used than the standard, they must be supplied as a named vector where the names correspond to the output of `billion_ind_codes()`.
`end_year`	End year(s) for contribution calculation, defaults to 2019 to 2025.
`iso3`	Column name of column with country ISO3 codes.