chore(docs): add Tobiko Cloud upgrade documentation

Author: newtonapple

docs/cloud/features/upgrade/upgrade-ui-custom-version.png

@@ -0,0 +1,52 @@
+# Upgrades
+
+Upgrading a Tobiko Cloud project can be done by going to `Settings > Upgrade`.
+If a new version is available for your project, you'll see an upgrade page like the one below.
+You can choose to upgrade to the latest version or specify a custom version.
+Clicking the **Upgrade Now** button and confirming will start the upgrade process.
+
+![Tobiko Cloud Upgrade Page](./upgrade/upgrade-ui-latest.png)
+
+!!! info "Upgrade Permissions"
+    Only users with `Admin` permissions can perform upgrades.
+
+!!! warning "Upgrade Preparations"
+    The upgrade process may take a few minutes to complete. During this time, your Tobiko Cloud project will be unavailable.
+    Any in-progress plans and runs will be aborted:
+
+    - Aborted plans will be stopped and must be recreated.
+    - Aborted runs will be automatically resumed shortly after the upgrade completes.
+
+    To avoid unexpected interruptions, please notify your team before starting the upgrade.
+
+## Custom Version
+
+Although it is recommended to always upgrade your Tobiko Cloud project to the latest version,
+there may be cases where a team needs to upgrade to a specific version.
+
+For example, a team might have separate staging and production projects.
+They may upgrade the staging project first, run tests, and only upgrade the production project after verifying that staging works as expected.
+If a new version is released during this testing period, the team may want to upgrade production to the same version used in staging.
+Custom version selection supports this workflow.
+
+To specify a custom version, select the **Custom** tab on the Upgrade page and enter the desired version in the text box.
+
+![Tobiko Cloud Upgrade Custom Version](./upgrade/upgrade-ui-custom-version.png)
+
+!!! info "Valid Custom Version"
+    Enter the custom version **without** the leading `v`.
+    The version must be valid and greater than the current version of the project.
+    If the custom version is not valid, an error message will be displayed.
+
+## Upgrade Progress
+
+After starting the upgrade, a progress page will be shown.
+Once the upgrade is complete, you’ll be automatically redirected back to the upgraded Tobiko Cloud project.
+
+![Tobiko Cloud Upgrade Progress](./upgrade/upgrade-ui-progress.png)
+
+## Project Already Up-to-Date
+
+If the project is already on the latest version, you’ll see a message like the one below.
+
+![Tobiko Cloud Upgrade Already Up-to-Date](./upgrade/upgrade-ui-up-to-date.png)

docs/cloud/features/upgrade/upgrade-ui-latest.png

@@ -126,6 +126,7 @@ nav:
         - cloud/features/security/single_sign_on.md
       - cloud/features/incident_reporting.md
       - cloud/features/xdb_diffing.md
+      - cloud/features/upgrades.md
 #      - Observability:
 #        - cloud/features/observability/overview.md
 #        - cloud/features/observability/model_freshness.md