feat: add database tables and API routes for agentic chat feature (#17570)

Backend portion of experimental `AgenticChat` feature:
- Adds database tables for chats and chat messages
- Adds functionality to stream messages from LLM providers using
`kylecarbs/aisdk-go`
- Adds API routes with relevant functionality (list, create, update
chats, insert chat message)
- Adds experiment `codersdk.AgenticChat`

---------

Co-authored-by: Kyle Carberry <kyle@carberry.com>

coderd/database/dump.sql

@@ -755,6 +755,32 @@ CREATE TABLE audit_logs (
     resource_icon text NOT NULL
 );
 
+CREATE TABLE chat_messages (
+    id bigint NOT NULL,
+    chat_id uuid NOT NULL,
+    created_at timestamp with time zone DEFAULT now() NOT NULL,
+    model text NOT NULL,
+    provider text NOT NULL,
+    content jsonb NOT NULL
+);
+
+CREATE SEQUENCE chat_messages_id_seq
+    START WITH 1
+    INCREMENT BY 1
+    NO MINVALUE
+    NO MAXVALUE
+    CACHE 1;
+
+ALTER SEQUENCE chat_messages_id_seq OWNED BY chat_messages.id;
+
+CREATE TABLE chats (
+    id uuid DEFAULT gen_random_uuid() NOT NULL,
+    owner_id uuid NOT NULL,
+    created_at timestamp with time zone DEFAULT now() NOT NULL,
+    updated_at timestamp with time zone DEFAULT now() NOT NULL,
+    title text NOT NULL
+);
+
 CREATE TABLE crypto_keys (
     feature crypto_key_feature NOT NULL,
     sequence integer NOT NULL,
@@ -2195,6 +2221,8 @@ CREATE VIEW workspaces_expanded AS
 
 COMMENT ON VIEW workspaces_expanded IS 'Joins in the display name information such as username, avatar, and organization name.';
 
+ALTER TABLE ONLY chat_messages ALTER COLUMN id SET DEFAULT nextval('chat_messages_id_seq'::regclass);
+
 ALTER TABLE ONLY licenses ALTER COLUMN id SET DEFAULT nextval('licenses_id_seq'::regclass);
 
 ALTER TABLE ONLY provisioner_job_logs ALTER COLUMN id SET DEFAULT nextval('provisioner_job_logs_id_seq'::regclass);
@@ -2216,6 +2244,12 @@ ALTER TABLE ONLY api_keys
 ALTER TABLE ONLY audit_logs
     ADD CONSTRAINT audit_logs_pkey PRIMARY KEY (id);
 
+ALTER TABLE ONLY chat_messages
+    ADD CONSTRAINT chat_messages_pkey PRIMARY KEY (id);
+
+ALTER TABLE ONLY chats
+    ADD CONSTRAINT chats_pkey PRIMARY KEY (id);
+
 ALTER TABLE ONLY crypto_keys
     ADD CONSTRAINT crypto_keys_pkey PRIMARY KEY (feature, sequence);
 
@@ -2699,6 +2733,12 @@ CREATE TRIGGER user_status_change_trigger AFTER INSERT OR UPDATE ON users FOR EA
 ALTER TABLE ONLY api_keys
     ADD CONSTRAINT api_keys_user_id_uuid_fkey FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE;
 
+ALTER TABLE ONLY chat_messages
+    ADD CONSTRAINT chat_messages_chat_id_fkey FOREIGN KEY (chat_id) REFERENCES chats(id) ON DELETE CASCADE;
+
+ALTER TABLE ONLY chats
+    ADD CONSTRAINT chats_owner_id_fkey FOREIGN KEY (owner_id) REFERENCES users(id) ON DELETE CASCADE;
+
 ALTER TABLE ONLY crypto_keys
     ADD CONSTRAINT crypto_keys_secret_key_id_fkey FOREIGN KEY (secret_key_id) REFERENCES dbcrypt_keys(active_key_digest);