OCPBUGS-38723: Add section for new roles for short lived credentials

** GCP Short lived credentials does not fill out certain fields in the GCP structure. This causes failures
when creating resources such as signed urls. In order to create these resources the user should add the
role Service Account User which has the permission "iam.serviceAccounts.signBlob".

Author: barbacbd

modules/installation-gcp-service-account.adoc

@@ -33,8 +33,6 @@ While making the service account an owner of the project is the easiest way to g
 . You can create the service account key in JSON format, or attach the service account to a GCP virtual machine.
 See link:https://cloud.google.com/iam/docs/creating-managing-service-account-keys#creating_service_account_keys[Creating service account keys] and link:https://cloud.google.com/compute/docs/access/create-enable-service-accounts-for-instances[Creating and enabling service accounts for instances] in the GCP documentation.
 +
-You must have a service account key or a virtual machine with an attached service account to create the cluster.
-+
 [NOTE]
 ====
 If you use a virtual machine with an attached service account to create your cluster, you must set `credentialsMode: Manual` in the `install-config.yaml` file before installation.

modules/minimum-required-permissions-ipi-gcp.adoc

@@ -186,6 +186,12 @@ If your organization’s security policies require a more restrictive set of per
 * `iam.roles.get`
 ====
 
+.Required permissions when authenticating without a service account key
+[%collapsible]
+====
+* `iam.serviceAccounts.signBlob`
+====
+
 .Optional Images permissions for installation
 [%collapsible]
 ====

modules/minimum-required-permissions-upi-gcp.adoc

@@ -187,6 +187,12 @@ If your organization’s security policies require a more restrictive set of per
 * `iam.roles.get`
 ====
 
+.Required permissions when authenticating without a service account key
+[%collapsible]
+====
+* `iam.serviceAccounts.signBlob`
+====
+
 .Required Images permissions for installation
 [%collapsible]
 ====