fixes #37474 - feat: enable updating ansible override values via api

[gardar]

As reported here:

https://community.theforeman.org/t/update-ansible-variable-overrides-over-the-api-gives-error/
and here:
https://projects.theforeman.org/issues/37474

[nofaralfasi]

I noticed two things:

1. When trying to update the value for a variable that doesn't have an override value, we get an error. We should catch that error and print an informative message to the user.
2. When a user without the required permissions tries to override a value, the necessary permissions are not specified in the error message.

[gardar]

I noticed two things:

1. When trying to update the value for a variable that doesn't have an override value, we get an error. We should catch that error and print an informative message to the user.

I was actually originally planning to modify the current POST method of the /ansible_override_values so that in addition to creating new overrides it would update existing ones. So rather than using POST for creating and PUT for updating the POST would be used for both. I would much prefer that approach myself but I decided to follow the design of the other api endpoints which use POST for creating and PUT for updating.
What are your thoughts? Can we use POST for both? Then we don't have to print a informative message to the user.

2. When a user without the required permissions tries to override a value, the necessary permissions are not specified in the error message.

In my experience this is actually the case for the other api endpoints as well, the necessary permissions are not specified in the error message.
Perhaps all the api endpoints should be updated with that regard in a separate PR?