migration: add callout for rescheduling mechanism (#6337)

## What are you changing in this pull request and why?
recently, the multicell team added a component to the in-app migration
guide which allows customers to postpone their account migration by up
to 45 days (this functionality is currently only available to enterprise
tier accounts).

as we begin migrating more enterprise accounts, we want our public
facing docs to highlight this for our users.



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---------

Co-authored-by: Matt Shaver <60105315+matthewshaver@users.noreply.github.com>

website/docs/docs/cloud/migration.md

@@ -15,6 +15,13 @@ Your account will be automatically migrated on or after its scheduled date. Howe
 
 ## Recommended actions
 
+:::info Rescheduling your migration
+
+If you're on the dbt Cloud Enterprise tier, you can postpone your account migration by up to 45 days. To reschedule your migration, navigate to **Account Settings** → **Migration guide**.
+
+For help, contact the dbt Support Team at [support@getdbt.com](mailto:support@getdbt.com).
+:::
+
 We highly recommended you take these actions:
 
 - Ensure pending user invitations are accepted or note outstanding invitations. Pending user invitations might be voided during the migration. You can resend user invitations after the migration is complete.