[keyserver] change reaction type from just like emoji to any emoji

Summary:
change reaction type from just like to any string. We will need to make this change so that any emoji can be used when creating a new reaction message

Depends on D6409
Linear Task: ENG-2776

Test Plan:
flow and this will be futher tested in subsequent diffs, additionally all the jest tests below passed

Reviewers: atul, tomek, ashoat

Reviewed By: ashoat

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D6398