Add Illumina NextSeq 2000 as Sequencing Platform valid value

[clarisse-lau]

Illumina NextSeq 2000 is used by the BU team for Bulk RNA sequencing. Add this (along with Illumina NextSeq 1000 ?) to the valid values for Sequencing Platform.

The center has submitted annotations under Illumina NextSeq so this is not a blocker, but providing the exact system would be preferred.