Image upload via admin api

Issue Summary

I'm writing a plugin uploading images from obsidian to ghost. When running the code bellow it triggers CORS due to the use of axios. See also https://forum.ghost.org/t/cors-using-admin-api-from-electron-app-obsidian/37743/6

To Reproduce

1. Code bellow and run the plugin. (Ignore if there's a parenthesis missing or something, I went back to try and reconstruct it).

	async function uploadImages(html: string) {
		// Find images that Ghost Upload supports
		let imageRegex = /!*\[\[(.*?)\]\]/g;
		let imagePromises = [];

		// Get full-path to images
		let imageDirectory: string;
		let adapter = app.vault.adapter;
		if (adapter instanceof FileSystemAdapter) {
			imageDirectory = adapter.getBasePath(); // Vault directory
			if (settings.screenshotsFolder) {
				imageDirectory = `${imageDirectory}${settings.screenshotsFolder}`;
			}
			if (frontmatter.imageDirectory) { // Extends the image directory
				imageDirectory = `${imageDirectory}${frontmatter.imageDirectory}`;
			}
		}
		console.log("Image Directory", imageDirectory);
		let result: RegExpExecArray | null; // Declare the 'result' variable

		while((result = imageRegex.exec(html)) !== null) {
			let file = `${imageDirectory}/${result[1]}`;

	                // Upload the image, using the original matched filename as a reference
	                imagePromises.push(api.images.upload({
		                ref: file,
		                file: file
	                }));
                }

                    return Promise
	                    .all(imagePromises)
	                    .then(images => {
		                    images.forEach(image => html = html.replace(image.ref, image.url));
		                    return html;
	                    });
                    }

2. Execute the plugin in obsidian and get the following:
   Access to XMLHttpRequest at 'http://localhost:2368/ghost/api/v4/admin/images/upload/' from origin 'app://obsidian.md' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

Maybe this is more of a feature request than a bug - nevertheless something annoying.

Start with the Admin API image-upload endpoint and its preflight response, using the Obsidian/Electron origin shown in the report. The issue names no repository file or test; done means the documented upload flow can be exercised from that origin without the reported CORS failure.