Forms: Add CSV file upload support (#46308)

Allow text/csv files to be uploaded via the unauthenticated file upload list, using forms file upload field.

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/20261844760

Upstream-Ref: Automattic/jetpack@117f45a

Author: simison

CHANGELOG.md

@@ -15,6 +15,7 @@ This is an alpha version! The changes listed here are not final.
 
 ### Changed
 - Add jetpack_forms_extra_webhooks filter and include feedback ID in jetpack_forms_before_webhook_request filter
+- Allow CSV files to be uploaded via contact forms
 - Forms: auto-generate webhook id so users don't have to fill it.
 - Forms: refactored how we retrieve form submission fields to send in the webhook payload.
 - Forms: track webhook requests done in wpcom infrastructure.

src/contact-form/class-contact-form-field.php

@@ -1473,6 +1473,7 @@ private function render_file_field( $id, $label, $class, $required, $required_fi
 				'odt'             => 'application/vnd.oasis.opendocument.text',
 				'ppsx'            => 'application/vnd.openxmlformats-officedocument.presentationml.slideshow',
 				'ppsm'            => 'application/vnd.ms-powerpoint.slideshow.macroEnabled.12',
+				'csv'             => 'text/csv',
 				'xla|xls|xlt|xlw' => 'application/vnd.ms-excel',
 				'xlsx'            => 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
 				'xlsm'            => 'application/vnd.ms-excel.sheet.macroEnabled.12',