Fix Incorrect agent_key Format in AgentManager::update_config Call in applyNode

[sophie-cluml]

In the applyNode GraphQL API of review-web, the AgentManager::update_config function is being called with an incorrect format for the agent_key. The function update_config expects the agent_key to be in the format of:

// note: this is pseudo code
format!("{}@{}", agent.key, node.profile.unwrap().hostname)

However, the current implementation only uses agent.key, without the "@" sign and the "hostname". So we need to correct it.