First action from ENG-9285. Addresses ENG-9286.

Added reducer for holders and action to store already-established holder in the store.
We use it in the blob service upload hook, to store the initial holder, which previously was forgotten

Inspired by D12949

Depends on D13401, D13402

• Reducer unit test
• Uploaded multimedia to a DM thread and used Redux Devtools to ensure the action was performed correctly