Subscription form: Move label out of email input

Right now, the label for the Subscription form email input is in the input itself. This is not great. We should move the label to be a proper label and instead of a placeholder in the email input.

Here is what it looks like now:


Instead, it should behave more like the Contact Form shown here:


This will possibly break some styles, but will be an improvement for accessibility.

Locate the Subscription form's email input and compare its current label and styling with the Contact Form shown in the issue. Move the label out of the input, remove the placeholder-style label, and verify that the resulting form remains usable and accessible without breaking its styles.

Written by the indexing model from the issue text.