feat: add backend logic for determining tasks tab visibility (#18401)

This PR implements the backend logic for determining if the Tasks tab
should be visible in the web UI as described in [the
RFC](https://www.notion.so/coderhq/Coder-Tasks-207d579be5928053ab68c8d9a4b59eaa?source=copy_link#210d579be5928013ab5acbe69a2f548b).

The frontend component will be added in a follow-up PR once the entire
Tasks backend is implemented so as not to break the dogfood environment
until then.

site/src/api/typesGenerated.ts

@@ -736,6 +736,7 @@ export interface DeploymentValues {
 	readonly additional_csp_policy?: string;
 	readonly workspace_hostname_suffix?: string;
 	readonly workspace_prebuilds?: PrebuildsConfig;
+	readonly hide_ai_tasks?: boolean;
 	readonly config?: string;
 	readonly write_config?: boolean;
 	readonly address?: string;