[BREAKING] feat/refactor/docs: multiple providers, large refactor, configurable ticking interval, fix for jwks endpoint has different host

[antonengelhardt]

Please describe your changes and why you made them

Multiple OpenID providers

• the plugin can now be configured to use multiple providers for token issuing and validation
• the discovery fetches all information from the configured providers, loads the jwks etc.
• if there is more than one provider, then the user can select a provider to authenticate with on a dedicated page. this happens with a callback (_wasm-oidc-plugin/provider-selection?authorize_with_provider=wwu&return_to=lw), which then redirect to the authorization_endpoint, because otherwise we would not be able to know which server sent the code in the code callback.
• if there is only one provider, the redirection will happen right away

Small features

• configurable ticking interval (ticking_interval_in_ms)
• logout path to clear cookies and end session (optional) as in #96
• get envoy request id and show it in the logs & error page when something fails #101

Refactor & fixes

• large refactor of the files and codebase (more to come)
• fix if open id providers had the jwks_uri exposed at a different host than the openid-configuration host
• get :scheme to parse url as in #98
• pretty print discovery and jwks responses when log level is debug

Does this PR introduce a breaking change?

[!WARNING] This PR introduces a breaking change: Please see envoy.yaml for the updated config structure

TODOs

• [x] Update k8s files
• [ ] Write a script to migrate config
• [x] Readme
• [ ] More comments, docs and logs
• [x] Error pages in html.rs
• [x] Include #98
• [x] Include #96

Other information and Screenshots (if appropriate)

🤫 It has darkmode

Linked

For #93

more to come