Rename addSyncedMetadata and removeSyncedMetadata action types to set and clear

Summary:
Thought this naming convention was cleaner. Matching the naming convention of operations on our other metadata data type.

Depends on D11626

Test Plan: flow check

Reviewers: atul, ginsu

Reviewed By: atul

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11627