Unsuccessful Secret Key Update and Remove

#### Issue details

when attempting to change or delete the cryptographic keys within the application, users experience a lack of feedback from the interface, resulting in an inability to perform these actions. In other words, a user cannot choose to apply the newly created secret key, while the Mission Planner software will keep using the previously created first secret key.

On the other hand, when the local key file in GCS (Mission Planner) is deleted, the UAV remains bound to the existing key, and as a result, the GCS is unable to verify signatures or control the UAV.

#### Version
Mission Planner 1.3.81

#### Platform
[ ] All
[ ] AntennaTracker
[ ] Copter
[ ✔️] Plane
[ ] Rover
[ ] Sub

#### Airframe type
SITL

#### Hardware type
NA

#### Logs
NA

Start by reproducing the secret-key update and removal flows in Mission Planner 1.3.81 using the Plane SITL setup described in the issue. Check what happens when a new key is selected and when the local GCS key file is deleted. Done means the interface gives useful feedback, key changes take effect, and deleting the local key does not leave the UAV bound without a recoverable verification path.

Written by the indexing model from the issue text.