Search: add enterprise discount nudges to our pricing pages.

### Impacted plugin

Jetpack

### What

We have discounts available for enterprise level customers, but they are hard to find.

### How

There are multiple places we should nudge users to contact us about enterprise tiers:
- emails nudging users to upgrade
- the Jetpack Search pricing UI in wp-admin
- the jetpack.com/upgrade/search page
- the jetpack.com/support/search page (probably in the FAQ)
- in the cart (maybe?)

Start by mapping the requested touchpoints: upgrade emails, the Jetpack Search pricing UI in wp-admin, jetpack.com/upgrade/search, jetpack.com/support/search, and the cart. Confirm where enterprise customers should be prompted to contact the team, then verify each relevant surface presents the approved nudge consistently and that the FAQ placement is appropriate.

Written by the indexing model from the issue text.