feat: agent metadata with custom collectors

migrations/sqlite/0000000_init.up.sql

@@ -2,7 +2,9 @@
 
 CREATE TABLE agents (
     id INTEGER PRIMARY KEY,
-    remote_id TEXT NOT NULL UNIQUE,
+    thumbprint TEXT UNIQUE,
+    keyset TEXT,
+    metadata TEXT,
     status INTEGER NOT NULL,
     created_at datetime NOT NULL,
     updated_at datetime NOT NULL
@@ -13,7 +15,7 @@ CREATE TABLE specs (
     agent_id INTEGER,
     name TEXT NOT NULL,
     revision INTEGER DEFAULT 0,
-    data TEXT, 
+    data TEXT,
     created_at datetime NOT NULL,
     updated_at datetime NOT NULL,
     FOREIGN KEY (agent_id) REFERENCES agents (id) ON DELETE CASCADE,