Once HTAN Portal and Google Big Query updated for CDS to GC change, update appropriate sections of manual

[jen-dfci]

Once HTAN Portal and BQ updates, change the following pages in the manual:

1. https://docs.humantumoratlas.org/data_access/portal/
2. https://docs.humantumoratlas.org/data_access/cds_gen3/
3. https://docs.humantumoratlas.org/data_access/cds_cgc/

[jen-dfci]

BQ notebook name and link updated in PR#92