[experiments] Algorithm picker misses a refresh functionality

When the user is configuring an experiment, it is not obvious that, if a block cannot be filled, they would need to create a new algorithm matching endpoint criteria.

It would be good to:

  1. If no algorithms match, then a button for creating a new algorithm is displayed to the right. It would be an extra feature if the algorithm new page is already displayed with the correct endpoint names.
  2. If the user is, after creating the algorithm, able to refresh the available algorithm list.
  3. In the case no algorithm is selected on the dropdown, make sure the word null is not displayed (this is actually a display bug).

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