Front-Channel Logout endpoint for OIDC

[vepatel]

Is your feature request related to a problem? Please describe.
I'd like to add Front-Channel Logout endpoint functionality through OIDC policy

Describe the solution you'd like
reference solution from njs implementation: nginxinc/nginx-openid-connect@1f5053b

[github-actions]

Hi @vepatel thanks for reporting!

Be sure to check out the docs and the Contributing Guidelines while you wait for a human to take a look at this 🙂

Cheers!

[vepatel]

@anderius re #7266 (comment)