Bundle couchbase database plugin with vault

[tomhjp]

The couchbase database plugin is a new secrets backend allowing vault to manage dynamic and static roles for instances of couchbase database. See the repo here for full details.

This PR bundles the new plugin into the vault binary, as we do with most other database plugins.

• Import plugin to the registry
• Add it to the gen_openapi.sh script
• go mod tidy and go mod vendor

I've also built vault from this PR and tested that I can enable and run the couchbase plugin:

tom:~ $ vault secrets enable database
Success! Enabled the database secrets engine at: database/
tom:~ $ vault write database/config/insecure-couchbase plugin_name=couchbase-database-plugin hosts=localhost username=Administrator password=password allowed_roles="*"
tom:~ $ vault write database/roles/insecure-couchbase-admin-role db_name=insecure-couchbase default_ttl=5m max_ttl=1h
Success! Data written to: database/roles/insecure-couchbase-admin-role
tom:~ $ vault read database/creds/insecure-couchbase-admin-role
Key                Value
---                -----
lease_id           database/creds/insecure-couchbase-admin-role/rgZP9Yk0jBuxTk5eawTpC9b3
lease_duration     5m
lease_renewable    true
password           A1a-ab2HuBC379yLslIk
username           v-root-insecure-couchbase-admin-role-1bdK1jAy4vbOR

[jasonodonnell]

LGTM pending using the right tag for the plugin.

[tomhjp]

LGTM pending using the right tag for the plugin.

Good point, done.