Cassandra Assets: improve examples and had astra-keyspace asset

[eolivelli]

Summary:

• move the example applications to use the new assets
• implement a new astra-keyspace, as for AstraDB we need some special handling with a different SDK and you also need the AstraCS token and the database name
• in the Astra DataSource we support now both username/password and clientId/secret, this is because by default the Astra UI calls them that way, it shows 3 fields: clientId, secret and token.
• Change the AssetManager API in order to allow to cache the DataSource

The new astra-keyspace works this way:

assets:
 - name: "products-keyspace"
    asset-type: "astra-keyspace"
    creation-mode: create-if-not-exists
    config:
      keyspace: "products"
      datasource: "AstraDBDatasource"

Unfortunately in order to make it work you must provide more configurations to the AstraDBDatasource

secrets.yaml

secrets:
  - name: astra
    id: astra
    data:
      secureBundle: "<file:secure-connect-database.zip>"            
      clientId: "qCZpZkEXtKiDGQlffHIhNAHT"
      secret: "xxxx"
      token: "AstraCS:xxxxxx"
      database: "xxxxxx"

configuration.yaml

configuration:
  resources:
    - type: "vector-database"
      name: "AstraDatasource"
      configuration:
        service: "astra"
        clientId: "{{{ secrets.astra.clientId }}}"
        secret: "{{{ secrets.astra.secret }}}"
        secureBundle: "{{{ secrets.astra.secureBundle }}}"
        token: "{{{ secrets.astra.token }}}"
        database: "{{{ secrets.astra.database }}}"

The values for "token" and for "database" are required only by the astra-keyspace asset, you don't need to configure them normally