[Feat]: Support multi-turn conversation

### Is your feature request related to a problem? Please describe.

Some interactions are multi-turn. For example the remote agent could require more information (`input-required` state). It would be nice to support this by allowing to reuse the same task id (if available).

### Describe the solution you'd like

Add a checkbox "reply" (reserve task id) next to the message textbox / "Send" button.

In case there is a task identifier (the `taskId` field should likely be populated):

* The checkbox is enabled
* If selected, the message that is sent will include the `taskId` of the previous message

This will allow testing multi-turn interactions.

### Describe alternatives you've considered

It is possible to use a script with custom code that does that but it would be giving up on the niceties of a2a-inspector.

One can "hack it" though the developer console, setting a break-point and manually modifying the sent message but this ugly.

### Additional context

_No response_

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct