Improve UX of new option for Secret Service in KWalletManager

I'm opening this issue so @teams/vdg can discuss UX improvements to a recently added option and settle on a solution:

The merge request !9 (merged) made by @ptrnine added an option to enable/disable the Secret Service DBus API, however, the way the option is presented doesn't make it clear what it is for or when you'd want to change it unless you have the technical knowledge to figure out what it means.

According to a comment in the merge request to support the Secrets API, this option was needed to make sure the user could use another wallet system since only one can use the secrets service at a time.

From a brief discussion in the VDG chat, we came up with two ideas:

The first one, suggested by @fox, is about showing the option to choose a default wallet manager from the Default Applications KCM.

Here's a mockup:

My original suggestion (I now prefer Christian's solution, but I'll add it here for the record), was to add an explanation to the option just like it is done in some other places on System Settings with the button. It could look like this:

This is just an example text