Create another Subpage for Migrating to SDK 4

Please create a second subpage under Compatibility for "Migrating to SDK 4 API" instead of the including it under SDK 3. It was very confusing to find.

Conversely, either the SDK 4 section of this page should be linked from the release notes page under the 4.0.0 header (https://docs.couchbase.com/nodejs-sdk/current/project-docs/sdk-release-notes.html#version-4-0-0-18-february-2022) or the notes from that section are reiterated in the 4.0.0 release update.

Background
I had a particular issue with a certificate path in the connection string but I did not know that because the only error I got was "invalid_argument". Instead, I traced through my code and eventually narrowed in on the connection string being a possible culprit. It was only then that I navigated to https://docs.couchbase.com/nodejs-sdk/current/howtos/managing-connections.html#connection-strings and found that this did, in fact, change in the 4.x update.

Reporter: Matt Manzi
E-mail: imyourmanzi1@gmail.com