feat: Add connection_timeout and troubleshooting_url to agent (#4937)

* feat: Add connection_timeout and troubleshooting_url to agent

This commit adds the connection timeout and troubleshooting url fields
to coder agents.

If an initial connection cannot be established within connection timeout
seconds, then the agent status will be marked as `"timeout"`.

The troubleshooting URL will be present, if configured in the Terraform
template, it can be presented to the user when the agent state is either
`"timeout"` or `"disconnected"`.

Fixes #4678

coderd/database/migrations/000072_add_agent_connection_timeout_and_troubleshooting_url.down.sql

@@ -0,0 +1,9 @@
+BEGIN;
+
+ALTER TABLE workspace_agents
+	DROP COLUMN connection_timeout_seconds;
+
+ALTER TABLE workspace_agents
+	DROP COLUMN troubleshooting_url;
+
+COMMIT;

coderd/database/migrations/000072_add_agent_connection_timeout_and_troubleshooting_url.up.sql

@@ -0,0 +1,13 @@
+BEGIN;
+
+ALTER TABLE workspace_agents
+	ADD COLUMN connection_timeout_seconds integer NOT NULL DEFAULT 0;
+
+COMMENT ON COLUMN workspace_agents.connection_timeout_seconds IS 'Connection timeout in seconds, 0 means disabled.';
+
+ALTER TABLE workspace_agents
+	ADD COLUMN troubleshooting_url text NOT NULL DEFAULT '';
+
+COMMENT ON COLUMN workspace_agents.troubleshooting_url IS 'URL for troubleshooting the agent.';
+
+COMMIT;