Connection String

• Part of the joined-up docs initiative - DOC-12275

Connection string and connecting to Couchbase are addressed practically in the SDK docs,
but there is no clear, central source of information on connecting to Couchbase, that applies to SDKs, connectors, tools, IDE plugins, mobile, and others:
Parameters that are needed, passing other parameters, ports, alternate addresses, `couchbase://`, `couchbases://`, `couchbase2://`, etc.