Today we require the `bootstrap.password` to be present in the keystore in order to
bootstrap xpack. With the addition of `keystore.seed` we have a randomly generated password
per node to do the bootstrapping. This will improve the initial user experience significantly
since the user doesn't need to create a keystore and add a password, they keystore is created
automatically unless already present and is always created with this random seed.
Relates to elastic/elasticsearch#26253
Original commit: elastic/x-pack-elasticsearch@5a984b4fd8