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/service/agent/mod.rs

@@ -0,0 +1,54 @@
+use nxmesh_proto::{
+    Ack, AgentMessage, HealthReport, MasterMessage, MetricsBatch,
+    agent_service_server::AgentService,
+};
+use tracing::warn;
+
+#[derive(Debug, Default)]
+pub struct AgentServerService {}
+
+#[async_trait::async_trait]
+impl AgentService for AgentServerService {
+    #[doc = " Server streaming response type for the Stream method."]
+    type StreamStream = tonic::codec::Streaming<MasterMessage>;
+
+    #[doc = " Stream establishes a persistent connection for real-time communication"]
+    #[allow(
+        mismatched_lifetime_syntaxes,
+        clippy::type_complexity,
+        clippy::type_repetition_in_bounds
+    )]
+    async fn stream(
+        &self,
+        request: tonic::Request<tonic::Streaming<AgentMessage>>,
+    ) -> Result<tonic::Response<Self::StreamStream>, tonic::Status> {
+        todo!()
+    }
+
+    #[doc = " ReportHealth sends a health report to the master"]
+    #[allow(
+        mismatched_lifetime_syntaxes,
+        clippy::type_complexity,
+        clippy::type_repetition_in_bounds
+    )]
+    async fn report_health(
+        &self,
+        request: tonic::Request<HealthReport>,
+    ) -> Result<tonic::Response<Ack>, tonic::Status> {
+        warn!("Received health report: {:?}", request.get_ref());
+        todo!()
+    }
+
+    #[doc = " ReportMetrics sends metrics batch to the master"]
+    #[allow(
+        mismatched_lifetime_syntaxes,
+        clippy::type_complexity,
+        clippy::type_repetition_in_bounds
+    )]
+    async fn report_metrics(
+        &self,
+        request: tonic::Request<MetricsBatch>,
+    ) -> Result<tonic::Response<Ack>, tonic::Status> {
+        todo!()
+    }
+}