New section for Existing Subscribers (#5933)

We are now offering a trial of all features in Cloud for our existing customers.  Doc updates describe the process and what to expect.

Author: danjohansenconsulting

docs/guides/cloud/free-trial.mdx

@@ -142,3 +142,25 @@ that Cypress Cloud provides!
   src="/img/guides/cloud/free-trial/trial-ci-setup.jpg"
   alt="Free trial CI setup"
 />
+
+## Existing Customers
+
+Are you already subscribed to a Cypress Cloud plan and would like to see and experience
+all features of Cypress Cloud during a trial period? If no changes have been
+made to your Cloud subscription for at least 90 days and you have not recently participated
+in a Cloud trial, then you will be able to opt-in to a trial of all features available in
+our Enterprise plan. An owner or admin in your organization will see a button to opt-in to
+this trial on the [Billing & Usage page](/guides/cloud/account-management/billing-and-usage).
+
+:::info
+
+<Icon name="question-circle" color="green" /> **Need immediate access?** If you do
+not see the trial opt-in button in your account and would like to immediately begin
+the trial of all Cloud features, please [contact us](mailto:[email protected]).
+
+:::
+
+The number of test results and users, as defined by your existing plan, will continue to
+be enforced during this trial period. All features available in Cloud will be
+unlocked for your organization to explore. At the end of this trial period, if you elect to
+remain in your current plan without any changes, no action on your part will be necessary.