Make AddAWSDynamoDBDistributedCache *only* add and not configure as well

The current approach is not ideal when you want to add the services separately to configuring them.

eg it would be useful to be able to configure in one place:
```
services
.AddOptions()
.Configure((options, config) => config.GetSection("DynamoDBCache").Bind(options))
.ValidateDataAnnotations();

// other configuring...
```

then be able to add the services somewhere else, allowing DI to resolve the options
```
services.AddAWSDynamoDBDistributedCache();

// add other services...
```

Locate the AddAWSDynamoDBDistributedCache entry point and inspect how it currently registers and configures services. Separate service registration from options configuration so callers can configure DynamoDBDistributedCacheOptions independently, then verify that AddAWSDynamoDBDistributedCache still resolves the configured options.

Written by the indexing model from the issue text.