Implement mission joining and leaving - Actions

[a-laarabi]

What?

• When a user clicks the "Join Mission" button, an action is dispatched to update the store.
• When a user clicks the "Leave Mission" button, an action is dispatched to update the store.

highlights 🔥

• I placed all my logic in the reducer.
• I despatched the action with the correct rocket ID as an argument.
• I set the reserved key to false.