subgraph 'execute to selected output nodes'

### Is there an existing issue for this?

- [x] I have searched the existing issues and checked the recent builds/commits

### What problem are you experiencing?

Subgraphs that have an output node inside of them do not have an 'execute to selected output nodes' button.

### When does this problem occur?

This happens when there is an output node inside a subgraph and the user is in the main graph.

### How often do you encounter this problem?

Occasionally

### How much does this problem affect your workflow?

Causes moderate inconvenience

### Current workarounds

keeping the output node outside of the subgraph and then running that nodes 'execute to selected output nodes' button is a workaround.

### Ideas for solutions (Optional)

I have not looked at the code, but but maybe marking a subgraph that contains output nodes as an output node

### Additional context

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-6630-subgraph-execute-to-selected-output-nodes-2a46d73d36508130a992c355ad0c3c08) by [Unito](https://www.unito.io)

The issue does not name a file, test, or entry point. Start by tracing the frontend implementation of the “execute to selected output nodes” action from the main graph and subgraph output-node handling; done means the action is available in the main graph when a subgraph contains an output node and the existing workflow works correctly.

Written by the indexing model from the issue text.