feat: Implement SSH Agent Connector and gRPC server

- Added `AgentConnectorTrait` and `AgentConnector` for managing agent connections.
- Introduced `SshAgentConnector` to handle SSH-related functionalities and start a gRPC server.
- Created database entities for `agents`, `certificates`, `organizations`, `public_key_revocations`, `setup_tokens`, `upstreams`, `users`, `virtual_hosts`, and `workspaces` using SeaORM.
- Developed `CertificateService` for managing certificate generation and retrieval.
- Implemented the main server logic to initialize the database connection and start the agent server.
- Configured development settings in `development.toml` for server and database connections.

apps/nxmesh-master/src/connector/agent/mod.rs

@@ -0,0 +1,40 @@
+use std::sync::Arc;
+
+use sea_orm::DatabaseConnection;
+use tonic::transport::Server;
+
+pub mod ssh;
+
+#[async_trait::async_trait]
+pub trait AgentConnectorTrait: Send + Sync {
+    async fn start_server(
+        &mut self,
+        settings: &crate::config::settings::Settings,
+        cert_service: Arc<dyn crate::service::certificate::CertificateService>,
+        connection: DatabaseConnection,
+    ) -> Result<(), Box<dyn std::error::Error + Send + Sync>>;
+}
+
+pub struct AgentConnector {
+    connector: Box<dyn AgentConnectorTrait>,
+}
+
+impl AgentConnector {
+    pub fn new(connector: Box<dyn AgentConnectorTrait>) -> Self {
+        Self { connector }
+    }
+}
+
+#[async_trait::async_trait]
+impl AgentConnectorTrait for AgentConnector {
+    async fn start_server(
+        &mut self,
+        settings: &crate::config::settings::Settings,
+        cert_service: Arc<dyn crate::service::certificate::CertificateService>,
+        connection: DatabaseConnection,
+    ) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
+        self.connector
+            .start_server(settings, cert_service, connection)
+            .await
+    }
+}