Create more FDC3 developer tools

FDC3 Workbench has been a great help for developers getting started with FDC3 and developing their first app integrations
See:
- https://github.com/finos/FDC3/blob/main/toolbox/fdc3-workbench/README.md
- https://fdc3.finos.org/toolbox/fdc3-workbench/ (needs to be run inside a desktop agent)

However, it takes up a lot of the screen - hence there is scope for FDC3 developer tools with other form factors, e.g. Widgets that can:
- Display context received on a channel
- Broadcast context on a channel on a button push
- Raise an intent on a button push
- Integrate with test frameworks to send or receive context or intents as part of a test
- etc.

Such tools can be implemented as:
- a standalone web project and later may be contributed to the FDC3 repo (toolbox folder)
- a refactor and update of the existing [FDC3 workbench project](https://github.com/finos/FDC3/tree/main/toolbox/fdc3-workbench) to create a responsive version (make it bigger to set-up context, make it smaller and it turns into a widget)
- or a combination (e.g. work with the FDC3 workbench in other ways: Workbench sets local storage with defined context examples, if hosted on the same domain widgets can read and use these context examples.

Start with toolbox/fdc3-workbench/README.md and inspect the existing toolbox/fdc3-workbench project. Compare the proposed widget forms and integration options, then define a focused tool and its scope before implementation. Done should mean the selected developer tool works in the stated FDC3 workflow and its usage is documented.

Written by the indexing model from the issue text.