Link to NOT_APPLICABLE docs in Shiny app UI.

[MelaniePhilofsky]

While reviewing our most recent, DQD v2.6, results. I came across some new checks with wording that might be misinterpreted by users reviewing the checks.

The checks have DQD STATUS = "NOT APPLICABLE".

The error message states the data are "missing". This is a little nit picky, but missing Implies the data should be there. However, these fields are not required. And we have purposely not populated the field (i.e. Payer_Plan_Period.sponsor_concept_id) since we do not have these data. I would suggest "missing" be replace by "not present".