Customizable keychain item name

[slevental]

Is your feature request related to a problem you're having? Please describe.
Currently library is storing the token within the keychain using the hardcoded name "auth" that is not customizable, we would like to test different versions (debug/release) of the application at the same machine and sometimes we found the system in a broken state, where the token is not correctly identified.

Describe the solution you'd like
We would like a bundle configuration control over the name of the keychain's item. Ideally, adding a new key to Info. list would control which name the keychain item should have. (right now, it's always equal to "auth", and it's set via kGTMAppAuthKeychainName const)

Describe alternatives you've considered
Alternatives would be using a different library for authorization

Additional context