docs: add TASK_INTERACTIVE environment variable documentation

Author: vmaerten

website/src/docs/reference/cli.md

@@ -332,6 +332,8 @@ Task automatically detects non-TTY environments (like CI pipelines) and
 skips prompts. This flag can also be set in `.taskrc.yml` to enable prompts
 by default.
 
+- **Environment variable**: [`TASK_INTERACTIVE`](./environment.md#task-interactive)
+
 ```bash
 task deploy --interactive
 ```

website/src/docs/reference/environment.md

@@ -75,6 +75,12 @@ variables. The priority order is: CLI flags > environment variables > config fil
 - **Default**: `false`
 - **Description**: Assume "yes" as answer to all prompts
 
+### `TASK_INTERACTIVE`
+
+- **Type**: `boolean` (`true`, `false`, `1`, `0`)
+- **Default**: `false`
+- **Description**: Prompt for missing required variables
+
 ### `TASK_TEMP_DIR`
 
 Defines the location of Task's temporary directory which is used for storing