[Fleet] Add cards for linking to file upload pages

[joshdover]

We need to register a card for the File Upload UI, similar to how we added cards for the sample data sets in #113200.

Title: File upload
Url: /app/home#/tutorial_directory/fileDataViz
Eui icon type: addDataApp
Category: upload_file
Description: Upload your file, analyze its data, and optionally import the data into an Elasticsearch index.

This card should only be registered when the upload file UI is registered, which happens here:

kibana/x-pack/plugins/data_visualizer/public/register_home.ts

Lines 16 to 22 in 940149c

	home.addData.registerAddDataTab({
	id: FILE_DATA_VIS_TAB_ID,
	name: i18n.translate('xpack.dataVisualizer.file.embeddedTabTitle', {
	defaultMessage: 'Upload file',
	}),
	component: FileDataVisualizerWrapper,
	});

Proposed way to solve this:

• Add customIntegrations to the optionalPlugins in x-pack/plugins/data_visualizer/kibana.json
• Update x-pack/plugins/data_visualizer/server/plugin.ts to call plugins.customIntegrations.registerCustomIntegration when plugins contains both home and customIntegrations (this way we only register this card if the UI it links to is also present).