improve mytoken cookie; refactor web client based config

cmd/mytoken-server/main.go

config/example-config.yaml

docker/example-docker-config.yaml

internal/config/config.go

internal/endpoints/configuration/configurationEndpoint.go

internal/oidc/authcode/authcode.go

internal/server/handlers.go

internal/server/web/sites/index.mustache

internal/server/web/static/js/login.js

internal/utils/cookies/cookies.go