[Doc] Update "Databricks Workspace Creator" permissions on gcp-workspace.md (databricks#4201)

## Changes
Match the corresponding (upcoming) changes to
https://docs.gcp.databricks.com/en/admin/cloud-configurations/gcp/permissions.html#required-permissions-for-the-workspace-creator

## Tests

- [ ] `make test` run locally
- [x] relevant change in `docs/` folder
- [ ] covered with integration tests in `internal/acceptance`
- [ ] relevant acceptance tests are passing
- [ ] using Go SDK

Author: vibhornana-db

docs/guides/gcp-workspace.md

@@ -57,6 +57,8 @@ resource "google_project_iam_custom_role" "workspace_creator" {
   permissions = [
     "iam.serviceAccounts.getIamPolicy",
     "iam.serviceAccounts.setIamPolicy",
+    "iam.serviceAccounts.create",
+    "iam.serviceAccounts.get",
     "iam.roles.create",
     "iam.roles.delete",
     "iam.roles.get",
@@ -68,8 +70,13 @@ resource "google_project_iam_custom_role" "workspace_creator" {
     "serviceusage.services.list",
     "serviceusage.services.enable",
     "compute.networks.get",
+    "compute.networks.updatePolicy",
     "compute.projects.get",
     "compute.subnetworks.get",
+    "compute.subnetworks.getIamPolicy",
+    "compute.subnetworks.setIamPolicy",
+    "compute.firewalls.get",
+    "compute.firewalls.create",
   ]
 }