Add combobox type functionality to UI when submitting a workflow

# Summary

Right now we have an enum which is great, however, in some cases being able to also specify a value not included in the enum would be nice.

I'm proposing adding a combobox style input which would function similar to an enum, but also allow for a custom value.

## Use Cases

In cases where you want to provide some default values to make it easy for most people to use, but also provide the ability to input something not found on the list.

An example of this might be that you have some tooling that generates an enum (for example a list of docker images). If you need to run the workflow against something not in the list you have to update the workflow.

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**Message from the maintainers**:

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The issue names no files, tests, or entry points. Start by locating the workflow-submission UI and its existing enum input, then define how custom values should behave and what coverage demonstrates that both predefined and custom values work.

Written by the indexing model from the issue text.