[ML] Analytics: Add starting state

[walterra]

This PR adds a starting state to analytics jobs.

• The UI code needs to be adapted to consider this state.
• We also need to check existing code wether any of the running states is considered properly. At the moment there's a bug for example where the Delete-button in the jobs list is available for running jobs because it only checks against the started state but not the others like reindexing or analyzing.

[elasticmachine]

Pinging @elastic/ml-ui (:ml)