Enhance custom query params for OIDC authZ endpoint

[shawnhankim]

As a Product Manager,

I want to more flexibly configure custom parameters for the OIDC authZ endpoint to be able to integrate with different business use cases per each IdP.

In addition to that, I want to synchronize the variable name between NGINX Plus and NGINX Management Suite.

• NGINX Plus OIDC: $oidc_authz_extra_args is merged (Dec/8/2022)
• NGINX Management Suite: $oidc_authz_path_params is released (Jul/20/2022)

AC:

• Refactor and enhance the existing reference implementation and the latest of PR to support following options:
  • option 1. Use built-in params
  • option 2. Extend extra params after the built-in params
  • option 3. Replace built-in params with custom params
• Revise the name from args to queryParams.
• Add key/values (e.g., $pkce_code_challenge, $nonce_hash) that can be configured as query params by customers for the OIDC authZ endpoint.

[shawnhankim]

Conflict w/ #22