REST Admin API to reactivate user #4740
Description
Is your feature request related to a problem? Please describe.
Account reactivation was implemented in matrix-org/matrix-authentication-service#2970 but only in the GraphQL API
Describe the solution you'd like
Implement a REST Admin API to reactivate a user
Describe alternatives you've considered
No permanent solution since the GraphQL API will be deprecated at some point
Additional context
User reactivation is used frequently by enterprise customers