[Can be deleted] Java: API layer with single commands (base, string, & void)

[acarbonetto]

Depends on valkey-io#717.

Issue #, if available:

API layer for: valkey-io#589

Description of changes:

In this PR, we're adding an API layer that creates a RedisClient using a RedisConfiguration.
Introduces the get & set & customCommand calls that allow a user to use the RedisClient.
This PR ensures that the type returned from the get/set/customCommand is correct for the type. A request using Exec returns a generic instead.

Out of Scope

• Connection and Command Managers that send the data to the backend Data Access layer (Java: Add managers layer to client valkey-io/valkey-glide#717)
• CreateClient configuration will be added in a follow-up PR.
• Transaction commands will be added in a follow-up PR.

Use cases

// connect to Redis
CompletableFuture<babushka.client.api.RedisClient> redisClientConnection =
    babushka.client.api.RedisClient.CreateClient(configuration);

// resolve the Future and get a RedisClient
babushka.client.api.RedisClient redisClient = redisClientConnection.get();

SetOptions setOptions = SetOptions.builder()
    .returnOldValue(true) // returns a String
    .build();
CompletableFuture<String> setRequest = redisClient.set("apples", "oranges", setOptions);
String oldValue = setRequest.get(); // returns a string unless .returnOldValue() is not true

CompletableFuture<String> getRequest = redisClient.get("apples");
String getValueStr = getRequest.get();
getValueStr == "oranges";  

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[acarbonetto]

duplicate of ConnectionManagerTest in managers.ConnectionManagerTest

[acarbonetto]

consider return type: maybe ClosingException? and we close the client?