[3.1.2 Backport] Hook up the reset resync code to a parameter that is passed into the resync endpoint

Currently we have code that can reset the resync process here ->  https://github.com/couchbase/sync_gateway/blob/9290abec176b50e7f996c6c340fd090101a8c473/db/background_mgr_resync_dcp.go#L70C35-L70C35 much like our attachment compaction code. The issue is there is nothing actually hooking the option up to the endpoint sop that a customer can use it. See here -> https://github.com/couchbase/sync_gateway/blob/246fde2151448dbbaa2f7c4a19d133c16abd2b29/rest/api.go#L318C25-L318C25

Ticket is to carry out the work to hook the both of them up.