Support Server-Side Encryption

[numberoverzero]

https://forums.aws.amazon.com/ann.jspa?annID=5434
https://aws.amazon.com/blogs/aws/new-encryption-at-rest-for-dynamodb/

CreateTable parameter is {"SSESpecification": {"Enabled": true}}
DescribeTable field is "SSEDescription": {"Status": STRING_ENUM} where STRING_ENUM is one of {ENABLING, ENABLED, DISABLING, DISABLED}

Like stream and ttl, This will be specified on the Meta object:

class User(BaseModel):
    id = Column(String, hash_key=True)
    expire_after = Column(Timestamp, dynamo_name="exp")

    class Meta:
        stream = {"include": {"new", "old"}}
        ttl = {"column": "expire_after"}
        encryption = {"enabled": True}

As with all optional meta config, when encryption isn't provided an existing value won't be validated. However a value is specified, it will be validated against the return value when binding the model.

[numberoverzero]

DescribeTable won't always return SSEDescription so sanitize_table_description needs to inject when missing with "Status": "DISABLED"