[SSO72] Add admin and service user silently

At the moment adding user via add-user.sh script outputs message info message and instruction to restart server:

Added 'admin' to '/opt/eap/standalone/configuration/keycloak-add-user.json', restart server to load user

add-user.sh script is used for Admin and Service user creation via environment variables in our scripts. Message after user creation may be confusing as there is actually no need to restart server since user creation happens prior to server start up. Our scripts should use add-user.sh script in silent mode (-s flag) and potentially replace log with our logging (log_info).

Affected scripts:

• add-sso-admin-user.sh
• add-sso-realm.sh