[Observability Rules] Support Re-ordering Actions

[BenB196]

Describe the feature:

When adding actions to a rule, the actions are added in a fixed order. It would be nice to be able to click/drag the actions around to re-order them.

Describe a specific use case for the feature:

When a rule has a large number of actions, it is sometimes helpful to have similar actions grouped together to make understanding what the rule does "easier". Today, if you want to reorder actions, you need to delete any actions that are out of order, and re-add them in the correct order.

[elasticmachine]

Pinging @elastic/response-ops (Team:ResponseOps)