is_eligible_continuation_maintenance: Is eligible continuation maintenance
In sutsabs/rwLoT: Line of Therapy Package

Is_elgible_continuation_maintenance checks if the line of therapy is a maintenance therapy for combo drug

is_eligible_continuation_maintenance(
  regimen,
  cases_maintenance,
  line_number,
  drug_group
)

`regimen`	a vector of drugs included in the line treatment regimen.
`cases_maintenance`	list of special cases for maintenance
`line_number`	a numeric value for the current line number
`drug_group`	a dataframe of drug summary table generated by `get_drug_summary`