Yes, you may add this to your profile as unpublished research. The question is which type to indicate - you may select, e.g., "Research proposal". If you do not know how to create a new page, consult RG's help Center (page "How to add research") for instructions how to add published or unpublished research to ResearchGate: https://help.researchgate.net/hc/en-us/articles/14293005132305