feat: add tests for dynamic parameters (#18679)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added support for a new testing attribute to the multi-select combobox
component, improving testability.
* Expanded mock data for dynamic parameters, covering a wider range of
input types and validation scenarios.

* **Bug Fixes**
* Improved loader and error handling on the experimental workspace
creation page to better display WebSocket errors.

* **Tests**
* Introduced comprehensive tests for the experimental workspace creation
page, including dynamic parameter updates, error handling, and form
submission scenarios.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Michael Smith <throwawayclover@gmail.com>

site/src/modules/workspaces/DynamicParameter/DynamicParameter.tsx

@@ -453,6 +453,7 @@ const ParameterField: FC<ParameterFieldProps> = ({
 		case "dropdown": {
 			return (
 				<Combobox
+					id={id}
 					value={value ?? ""}
 					onSelect={(value) => onChange(value)}
 					options={parameter.options.map((option) => ({
@@ -497,7 +498,10 @@ const ParameterField: FC<ParameterFieldProps> = ({
 
 			return (
 				<MultiSelectCombobox
-					inputProps={{ id }}
+					inputProps={{
+						id: id,
+					}}
+					data-testid={`multiselect-${parameter.name}`}
 					options={options}
 					defaultOptions={selectedOptions}
 					onChange={(newValues) => {