Returns EncryptionMaterials which the caller can use for encryption. Each
implementation of EncryptionMaterialsProvider can choose its own strategy
for loading encryption material. For example, an implementation might
load encryption material from an existing key management system, or load
new encryption material when keys are rotated.
Forces this encryption materials provider to refresh its encryption
material. For many implementations of encryption materials provider, this
may simply be a no-op, such as any encryption materials provider
implementation that vends static/non-changing encryption material. For
other implementations that vend different encryption material throughout
their lifetime, this method should force the encryption materials
provider to refresh its encryption material.