Make error reporting more specific to improve messaging towards clients

[petrdvorak]

Currently, we report all errors via a single error code, POWER_AUTH_ACTIVATION_INVALID, which makes debugging difficult. It would be helpful to distinguish error messages for certain specific situations, for example:

• Invalid activation OTP was used with a correct activation code
• Valid activation code not found, as it expired or was not present
• Technical error occurred during activation
• Activation code was issued for a different application
• Activation code was issued for the correct activation, but the version is not supported
• ...