Couchbase Lite 1.x: Update REST POST _replicate API

First comment:

According to forum post, https://forums.couchbase.com/t/how-to-sync-a-specific-channel-with-ionic2-couchbase-lite-2-0-and-sync-gateway-1-5/14300/4 , the following needs to be specified for filtering on channels
"In the POST to start the replication, add the JSON properties: "filter":"sync_gateway/bychannel", "channels":"ABC,NBC,CNN,FOX"

The current documentation needs to be updated accordingly https://developer.couchbase.com/documentation/mobile/1.4/references/couchbase-lite/rest-api/index.html?v=1.4#/server/post__replicate

see other comments: https://github.com/couchbaselabs/couchbase-mobile-portal/issues/815