Adds instructions for customers to complete their AWS annual subscription registration (#990)

See original PR here: elastic/cloud#139303
Preview is here:
https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/990/deploy-manage/deploy/elastic-cloud/complete-registration-of-an-annual-subscription-on-aws-marketplace

I'm not sure if this should be marked as `hidden` but I did it to follow
similar marketplace docs

---------

Co-authored-by: florent-leborgne <[email protected]>

Author: kwabena-ansah

deploy-manage/deploy/elastic-cloud/complete-registration-of-an-annual-subscription-on-aws-marketplace.md

@@ -0,0 +1,28 @@
+---
+applies_to:
+  deployment:
+    ess: ga
+  serverless: ga
+mapped_pages:
+  - https://www.elastic.co/guide/en/cloud/current/ec-marketplace-aws-prepaid-signup.html
+---
+
+# Complete the registration of an annual subscription on AWS Marketplace [ec-marketplace-aws-prepaid-signup]
+
+Follow the instructions on this page to complete the registration process for an Elastic Cloud annual subscription on AWS Marketplace.
+
+## Accept your offer and complete registration
+
+1. Log in to the AWS console on the account that you will use to accept the Annual Private Offer.
+
+2. Follow the offer URL provided by Elastic and accept the annual subscription.
+
+   :::{image} /deploy-manage/images/aws-accept-prepaid-offer.png
+   :alt: Accept a prepaid offer
+   :::
+
+3. After accepting the offer, select **Set up your account** to complete the registration process.
+
+   :::{image} /deploy-manage/images/aws-complete-registration.png
+   :alt: Complete registration
+   :::

deploy-manage/images/aws-accept-prepaid-offer.png

@@ -11,6 +11,7 @@ toc:
               - file: deploy/elastic-cloud/subscribe-from-marketplace.md
                 children:
                   - hidden: deploy/elastic-cloud/create-monthly-pay-as-you-go-subscription-on-aws-marketplace.md
+                  - hidden: deploy/elastic-cloud/complete-registration-of-an-annual-subscription-on-aws-marketplace.md
                   - hidden: deploy/elastic-cloud/azure-marketplace-pricing.md
                   - hidden: deploy/elastic-cloud/create-monthly-pay-as-you-go-subscription-on-gcp-marketplace.md
                   - file: deploy/elastic-cloud/aws-marketplace.md