Add authenticator configuration import documentation

[tegha-romeo]

Documentation for handling authenticatorConfig exports where internal Keycloak IDs are ignored by keycloak-config-cli. Users export configurations with UUIDs, but keycloak-config-cli only processes alias fields, causing authenticator settings to be missing during import.

Problem:

Exported configurations contain internal Keycloak UUIDs in authenticatorConfig
keycloak-config-cli ignores id field and only uses alias
Authenticator settings appear missing after import
Users don't understand why configurations don't apply