mutate_primary_key: Adds primary key to dataframe in position 1
In patelm9/somersault2:

Adds primary key to dataframe in position 1

mutate_primary_key(
  dataframe,
  pkey_column_name,
  starting_number = NULL,
  width_left_pad_with_zero = NULL,
  prefix = NULL
)

`pkey_column_name`	name of pkey column
`starting_number`	optional starting number for the primary key
`width_left_pad_with_zero`	integer of the number of leading zeros desired. NULL by default.
`prefix`	prefix desired with starting_number + left padding with zeros (if not NULL)