add guest mode

CHANGELOG.md

internal/config/config.go

internal/endpoints/configuration/configurationEndpoint.go

internal/endpoints/federation/entityStatement.go

internal/endpoints/guestmode/guestmode.go

internal/endpoints/settings/settings.go

internal/server/api.go

internal/server/middlerwares.go

internal/server/paths/paths.go

internal/server/routes/routes.go

internal/server/server.go