See https://wordpress.stackexchange.com/q/351867/137402 for details.

metabox-option.php

<?php
function add_image_link()
{
	add_meta_box(
		'image_link_box',
		'Link image to url',
		'image_link_field',
		'attachment'
	);
}
add_action( 'add_meta_boxes_attachment', 'add_image_link' );

function image_link_field( $post )
{
	?>
	<label for="image-link">Link URL</label>
	<input type="text" name="image_link" id="image-link" class="postbox" value="<?php
		echo esc_attr( get_post_meta( $post->ID, 'image_link_url', true ) ); ?>">
	<?php
}

function save_image_link( $post_id )
{
	if ( array_key_exists( 'image_link', $_POST ) ) {
		update_post_meta(
			$post_id,
			'image_link_url',
			sanitize_text_field( $_POST['image_link'] )
		);
	}
}
add_action( 'edit_attachment', 'save_image_link' );

non-metabox-option.php

<?php
// This part adds the custom field to the dialog.
add_filter( 'attachment_fields_to_edit', function ( $form_fields, $post ) {
	$form_fields['image_link'] = [
		'label' => 'Link to image URL',
		'value' => get_post_meta( $post->ID, 'image_link_url', true ),
	];

	return $form_fields;
}, 10, 2 );

// This part saves the field as a meta data.
add_filter( 'attachment_fields_to_save', function ( $post, $attachment ) {
	if ( isset( $attachment['image_link'] ) ) {
		$meta_input = isset( $post['meta_input'] ) ?
			(array) $post['meta_input'] : [];

		$meta_input['image_link_url'] = $attachment['image_link'];

		$post['meta_input'] = $meta_input;
	}

	return $post;
}, 10, 2 );