Java - Add custom command interface; and BaseCommands

[acarbonetto]

Issue #, if available:

API layer for: #589

Description of changes:

In this PR, we are adding basic infrastructure for commands, including the custom command that takes any command type and set of arguments, and returns an Object.

The Redis value_from_pointer is called to convert the value form a Rust objects to Java objects, so the FFI calls for complex objects are necessary for converting from complex objects.

Example:

CompletableFuture<RedisClient> createClientRequest = RedisClient.CreateClient(config); 

try (RedisClient client = createClientRequest.get()) 
{
      Object customGetMyKey = client.customCommand(new String[]{"get", "myKey"}).get();
      System.out.println("Glide CUSTOM_COMMAND(get, myKey): " + customGetMyKey);

      Object customGetInvalid = client.customCommand(new String[]{"get", "invalid"}).get();
      System.out.println("Glide CUSTOM_COMMAND(get, invalid): " + customGetInvalid);

} catch (ExecutionException executionException) {
    if (executionException.getCause() instanceOf RedisException) {
         // try again
  }
}

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[shachlanAmazon]

if the interface is public to the use, this will also be public to the user. Why do we want to expose this?

[acarbonetto]

Good question. I can hide this from the user, like RedisValueResolver::valueFromPointer is not being exposed.
This also applies to BaseCommandResponseResolver class?