feat: move step-ca into a plugin (C4)

plugins/step-ca/migrations/mysql/0001_create_certs.sql

@@ -0,0 +1,16 @@
+-- step-ca 0001: create_certs
+-- Generated by termix-plugin migrations. Review before committing.
+
+CREATE TABLE IF NOT EXISTS `p_step_ca_certs` (
+  `id` int AUTO_INCREMENT PRIMARY KEY,
+  `user_id` varchar(255) NOT NULL,
+  `host_id` int NOT NULL,
+  `ssh_cert` text NOT NULL,
+  `private_key` text NOT NULL,
+  `email` text,
+  `created_at` text NOT NULL DEFAULT (CURRENT_TIMESTAMP),
+  `expires_at` varchar(255) NOT NULL,
+  FOREIGN KEY (`user_id`) REFERENCES `users` (`id`) ON DELETE CASCADE,
+  FOREIGN KEY (`host_id`) REFERENCES `ssh_data` (`id`) ON DELETE CASCADE
+);
+CREATE UNIQUE INDEX `idx_step_ca_certs_user_host` ON `p_step_ca_certs` (`user_id`, `host_id`);