[Feature Request]: Allow for tooltips to be specified on subgraph inputs and outputs

### Is there an existing issue for this?

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

### What would your feature do ?

Tooltips are very useful in a lot of nodes to explain what each input/output does and how to use it, such as on the core ksampler node. Subgraph nodes can get pretty complex, and would require some widgets and inputs that need some explaining for internal documentation.

Let's say for instance, I have some complicated setup such as these two hiresfix ksampler nodes that can be switched between:

Rather than needing notes to explain some settings, I feel like it would be more convenient if I could already state how each input and output should be setup, what it's used for, etc.

### Proposed workflow

When implemented, should be able to be accessed as follows:

1. Go into a subgraph
2. Right click on any subgraph input/output
3. Click on "tooltip for _input/output name_"
4. Type out a tooltip to appear when the input/output is hovered over

### Additional information

_No response_

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-4582-Feature-Request-Allow-for-tooltips-to-be-specified-on-subgraph-inputs-23f6d73d365081f39089d175e8a0d6b9) by [Unito](https://www.unito.io)