[ML] Add data frame create_time and version

[sophiec20]

Understanding when the data frame is created is useful for operational management so we understand how long a job has existed and for filtering out job messages that were applicable to a prior incarnation of the job.

Understanding the version of elasticsearch that the data frame was created on, will help us with support and bwc fixes.

Please add to the create_time and version to GET _data_frame/transforms/blah - this follows how we use the immutable value create_time and job_version with anomaly detection.

(Also, consider how we tolerate fields like this if it were to be supplied when creating a data frame. i.e. create_time and version can be safely ignored even though they appear to be part of the config.)

[elasticmachine]

Pinging @elastic/ml-core