Pledge Management: Add "request link" form to the manage pledge (#126)

When a pledge is selected but the auth token is missing/incorrect, show the email form. Like on the pledge page, submitting the correct email will trigger a new auth token + link to be emailed to the pledge manager. This makes for a clearer path for re-requesting a valid link.

Fixes #114

plugins/wporg-5ftf/views/form-request-manage-link.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace WordPressDotOrg\FiveForTheFuture\View;
+use WordPressDotOrg\FiveForTheFuture\Pledge;
+
+defined( 'WPINC' ) || die();
+
+$pledge_id = ( Pledge\CPT_ID === get_post_type() ) ? get_post()->ID : absint( $_REQUEST['pledge_id'] ?? 0 );
+?>
+
+<form method="post" class="pledge-email-form">
+	<input type="hidden" name="pledge_id" value="<?php echo esc_attr( $pledge_id ); ?>" />
+
+	<label for="pledge_admin_address">
+		<?php esc_html_e( 'Email Address', 'wporg-5ftf' ); ?>
+	</label>
+
+	<input
+		id="pledge_admin_address"
+		name="pledge_admin_address"
+		type="email"
+		required
+		value=""
+	/>
+
+	<div class="message"></div>
+
+	<input
+		type="submit"
+		class="button"
+		name="get_manage_pledge_link"
+		value="<?php esc_attr_e( 'Submit', 'wporg-5ftf' ); ?>"
+	/>
+</form>