Economy mail content changes

[karlchillmaid]

Do not deploy these changes until we launch Economy mail

We need to update the letter pricing and delivery times information to help explain Economy Mail.

This PR reformats the delivery times information as a table.

It also adds some contextual content to the Pricing and Delivery times pages.

This is the MVP we agreed for launch.

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Extras:

• [x] check that the new ‘Economy mail’ column in the pricing page table will happen as part of the database update
• [x] find a way to make screenreaders to announce the ‘Prices do not include VAT’ line as part of the table

[kr8n3r]

putting "Letter pricing. Prices do not include VAT." in the caption text might be the simplest option

[kr8n3r]

changes look good. See https://github.com/alphagov/notifications-admin/pull/5422#issuecomment-2830665805 for my suggestion on adding wording to the (invisible) table caption.

As I've pushed changes, someone else will need to 🟢

Edit: I have squashed the commits into useful chunks

[klssmith]

Is it ok for the delivery times to be displayed now, or does this need to wait until the feature is live?

[karlchillmaid]

@klssmith I assume we wouldn’t publish the updated delivery times until Economy mail is actually ready (or thereabouts) – but I can check with JW.

[karlchillmaid]

@klssmith the answer from JW is that we need to wait until Economy mail is ready to launch before deploying the changes in this PR.