add optional sequence field

[JohnRDOrazio]

Who would have known CodeRabbit knew so much about the Catholic Liturgy! It doesn't get everything spot on, but does have some interesting suggestions. For example:

Add optional “sequence” field (Easter Day).

Easter Sunday has the Victimae paschali laudes sequence (optional). Adding a field prevents loss of data.

         "day": {
             "first_reading": "",
             "responsorial_psalm": "",
             "second_reading": "",
             "alleluia_verse": "",
-            "gospel": ""
+            "gospel": "",
+            "sequence": ""
         },

This could be considered I suppose. Though it's not a scriptural reference like the rest of the keys involved in the lectionary structures, we could still consider adding a sequence field somewhere, if not in the lectionary readings, at least somewhere in the Liturgical Event output. Also Corpus Christi and Pentecost have sequences.