Migrate from couchbase/go-couchbase to couchbase/gocb

[reimda]

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.

[powersj]

next steps: look into the migration to the new library