Migrate from couchbase/go-couchbase to couchbase/gocb

Couchbase provides two go client modules. couchbase/gocb is the current official module and couchbase/go-couchbase is an older unofficial module.

The telegraf couchbase input uses couchbase/go-couchbase. We have recently had to work around missing functionality (#9032) and insecure code (#9485) in it.

Telegraf should switch to gocb because it is the official supported module.

There is an old closed issue to switch to gocb (#2418). At the time of that issue the gocb module was new and didn't have functionality telegraf needed. We should revisit this now that time has past and gocb has matured.

Start with Telegraf's Couchbase input and inspect its current use of couchbase/go-couchbase, then read issues #9032 and #9485 for functionality and security constraints. Revisit issue #2418 and verify that the input can use couchbase/gocb while retaining the required behavior and resolving the cited limitations.

Written by the indexing model from the issue text.