docs: add docs explaining each keyring trace flag

Author: mattsb42-aws

src/aws_encryption_sdk/identifiers.py

@@ -340,8 +340,16 @@ class KeyringTraceFlagValue(object):
 
         name = attr.ib()
 
+    #: A flag to represent that a keyring has generated a plaintext data key.
     GENERATED_DATA_KEY = KeyringTraceFlagValue("GENERATED_DATA_KEY")
+    #: A flag to represent that a keyring has created an encrypted data key.
     ENCRYPTED_DATA_KEY = KeyringTraceFlagValue("ENCRYPTED_DATA_KEY")
+    #: A flag to represent that a keyring has obtained
+    #: the corresponding plaintext data key from an encrypted data key.
     DECRYPTED_DATA_KEY = KeyringTraceFlagValue("DECRYPTED_DATA_KEY")
+    #: A flag to represent that the keyring has cryptographically
+    #: bound the encryption context to a newly created encrypted data key.
     SIGNED_ENCRYPTION_CONTEXT = KeyringTraceFlagValue("SIGNED_ENCRYPTION_CONTEXT")
+    #: A flag to represent that the keyring has verified that an encrypted
+    #: data key was originally created with a particular encryption context.
     VERIFIED_ENCRYPTION_CONTEXT = KeyringTraceFlagValue("VERIFIED_ENCRYPTION_CONTEXT")