useExpiringTokens should be TypeBool

[TJM]

          > Learned something... ![Screenshot 2023-04-26 at 8 46 13 AM](https://user-images.githubusercontent.com/1641316/234613903-dbc6318d-d31e-4bd2-ba69-8c5f63a65f59.png)

We don't need this case statement to check for bool, because no matter what we submit, it comes out as a string? although this feels like a bug to me :)

Most likely because the attribute is defined as TypeString (https://github.com/jfrog/artifactory-secrets-plugin/blob/master/path_config.go#L33) 😄

Instead we should use TypeBool.

Originally posted by @alexhung in #88 (comment)