Add couchbase govk

[peczenyj]

This PR add supports for couchbase using gocb api version 2

To be possible run the tests you have two options

1. starts couchbase and set the following env vars:

• COUCHBASE_SERVER must contains the connection string example couchbase://localhost
• COUCHBASE_BUCKET must contains the name of the bucket to test
• COUCHBASE_USERNAME & COUCHBASE_PASSWORD must contains the user and pass needed to access the couchbase

This can be done following this procedure using docker

2. by running the tests with a bigger timeout (most of the time) and using the integration tag like in the example below. This integration tests starts a local container using github.com/testcontainers/testcontainers-go (you can check here and here how it works.

$ go test -v -timeout=600s -tags=integration ./...
2024/05/29 14:34:30 github.com/testcontainers/testcontainers-go - Connected to docker: 
  Server Version: 26.1.3
  API Version: 1.44
  Operating System: Ubuntu 24.04 LTS
  Total Memory: 15806 MB
  Resolved Docker Host: unix:///var/run/docker.sock
  Resolved Docker Socket Path: /var/run/docker.sock
  Test SessionID: 272a8f169a1a0cac2aa669bf15c7affb5f0c82e8c53b6e656244dcda14340428
  Test ProcessID: 1a1ef910-978e-44d5-8557-2c6a73ac2160
2024/05/29 14:34:30 🐳 Creating container for image testcontainers/ryuk:0.7.0
2024/05/29 14:34:30 ✅ Container created: 84ddc12dec3d
2024/05/29 14:34:30 🐳 Starting container: 84ddc12dec3d
2024/05/29 14:34:30 ✅ Container started: 84ddc12dec3d
2024/05/29 14:34:30 🚧 Waiting for container id 84ddc12dec3d image: testcontainers/ryuk:0.7.0. Waiting for: &{Port:8080/tcp timeout:<nil> PollInterval:100ms}
2024/05/29 14:34:30 🔔 Container is ready: 84ddc12dec3d
2024/05/29 14:34:30 🐳 Creating container for image couchbase:community-7.1.1
2024/05/29 14:34:30 ✅ Container created: 54dda7abeb27
2024/05/29 14:34:30 🐳 Starting container: 54dda7abeb27
2024/05/29 14:34:31 ✅ Container started: 54dda7abeb27
2024/05/29 14:34:31 🔔 Container is ready: 54dda7abeb27
=== RUN   TestClient
    couchbase_test.go:20: checking for couchbase connection string on env var "COUCHBASE_SERVER"
=== RUN   TestClient/Test_client_with_codec_JSON
=== RUN   TestClient/Test_client_with_codec_Gob
--- PASS: TestClient (0.02s)
    --- PASS: TestClient/Test_client_with_codec_JSON (0.01s)
    --- PASS: TestClient/Test_client_with_codec_Gob (0.01s)
PASS
2024/05/29 14:34:57 🐳 Terminating container: 54dda7abeb27
2024/05/29 14:34:57 🚫 Container terminated: 54dda7abeb27
ok  	github.com/philippgille/gokv/couchbase	27.600s

if there is no env var COUCHBASE_SERVER set, the tests will be skipped.