Add option to change keyname for idtoken generation

[mmascher]

Is your feature request related to a problem? Please describe. The default keyname is FRONTEND and there is not way to change it. Changing the name is required if it has been compromised and you want to invalidate all the existing tokens (new tokens cannot have the same kid)

Describe the solution you'd like Allow to change the kid parameters of the idtokens used to connect back to the pool.

Info (please complete the following information):

• Priority: high
• Stakeholder: CMS
• Component: frontend