Add Couchdb connector docs

[dhmlau]

Suggestion

Under the Connector References, there is no info on the CouchDB connector (loopback-connector-couchdb2), even though the lb4 datsource has this option.

Acceptance criteria

• add an entry for CouchDB under Connector Reference in LB3 docs
  • update the update-readmes.sh file to get the couchdb readme
• add an entry for CouchDB under Connector Reference in LB4 docs
• update CouchCB readme with LB4 specific configuration

[dhmlau]

FYI - issue reported by a community user

[agnes512]

Met all acceptance criteria. Closing as done