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/db/mod.rs

@@ -0,0 +1,11 @@
+use sea_orm::{Database, DatabaseConnection};
+
+pub mod entities;
+
+pub(crate) async fn establish_connection(
+    url: &str,
+) -> Result<DatabaseConnection, Box<dyn std::error::Error + Send + Sync>> {
+    Database::connect(url)
+        .await
+        .map_err(|e| format!("Failed to connect to database: {}", e).into())
+}