chore: combine keyvalue provider into couchbase provider

[jamesstocktonj1]

Description

• combine the example/wasi-keyvalue with the root of the project (provider now exports the wrpc:keyvalue interface)
• new project structure to separate the link creation from the wasmcloud:couchbase and wrpc:keyvalue handlers
• add the http-keyvalue-counter-rust endpoint to the example wadm.yaml

New Project Structure

├── provider
│   ├── couchbase            // implements the wasmcloud:couchbase interfaces
│   ├── keyvalue             // implements the wrpc:keyvalue interfaces
│   └── provider.go          // handles link creation/deletion and couchbase connections
└── main.go