[BUG] Slot rules in Training Module not functioning as intended

[jaX10bt]

Bug description:
When creating/modifying a rule that checks slots using slot_was_set, the Rasa rules syntax is broken due to a missing hyphen (-) before the slot name. This is an example of a broken rule:

  - rule: common_teenus_rk_hääletus_viimased
    steps:
      - slot_was_set:
          rk_hääletused: true
      - intent: common_teenus_rk_hääletus
      - action: utter_common_teenus_rk_hääletus_viimased
      - action: action_restart

Expected behavior:
This is how the rule should be:

  - rule: common_teenus_rk_hääletus_viimased
    steps:
      - slot_was_set:
          - rk_hääletused: true
      - intent: common_teenus_rk_hääletus
      - action: utter_common_teenus_rk_hääletus_viimased
      - action: action_restart

Screenshots:

Additional information:
When looking at the http response, a rule that is not broken has the slot name and value in an array ({slot_was_set: [{rk_hääletused: true}]}), while for a broken rule that is not the case ({slot_was_set: {rk_hääletused: true}})

[ExiRain]

Wrapped returning value for ruleset into array looks good for provided case:

#773