Fix pydantic error when note missing on link in jsonb

[jessemortenson]

We have a lot of data that does not have a note for each link. Also many EventMedia rows are missing offset.

Currently requests for VA events are returning 500 due to this error:

10 validation errors for Event
agenda -> 0 -> media -> 0 -> offset
  none is not an allowed value (type=type_error.none.not_allowed)
agenda -> 0 -> media -> 0 -> links -> 0 -> note
  field required (type=value_error.missing)
agenda -> 0 -> media -> 1 -> offset
  none is not an allowed value (type=type_error.none.not_allowed)
agenda -> 0 -> media -> 1 -> links -> 0 -> note
  field required (type=value_error.missing)
agenda -> 0 -> media -> 2 -> offset
  none is not an allowed value (type=type_error.none.not_allowed)
agenda -> 0 -> media -> 2 -> links -> 0 -> note
  field required (type=value_error.missing)
agenda -> 0 -> media -> 3 -> offset
  none is not an allowed value (type=type_error.none.not_allowed)
agenda -> 0 -> media -> 3 -> links -> 0 -> note
  field required (type=value_error.missing)
agenda -> 0 -> media -> 4 -> offset
  none is not an allowed value (type=type_error.none.not_allowed)
agenda -> 0 -> media -> 4 -> links -> 0 -> note
  field required (type=value_error.missing)