Update docs with new Cloud KMS Viewer role

The addition of the new Cloud KMS Viewer IAM role renders the Cloud
KMS Admin role obsolete. This commit updates documentation to refer
to the Cloud KMS Viewer role, which grants a more limited subset of
permissions while still allowing STET to look up key metadata.

PiperOrigin-RevId: 401865645
Change-Id: Ibebe97150d47748d8f18584ab45c60949ab0a9a0

docs/quickstart_guide.md

@@ -20,14 +20,12 @@ Cloud KMS/EKM.
     account creation, add the following roles:
     *   **Service Account Token Creator**
         *   This is needed so that the service account can generate OIDC tokens
-            required to authenticate with CCKM.
-    *   **Cloud KMS Admin**
+            required to authenticate with EKMs.
+    *   **Cloud KMS Viewer**
         *   This is needed to query Cloud KMS for
-            [key metadata](https://cloud.google.com/kms/docs/reference/permissions-and-roles")
+            [key metadata](https://cloud.google.com/kms/docs/reference/permissions-and-roles)
             which applies to both keys stored in Cloud KMS and also external
             keys.
-            *   Note: The Cloud KMS Admin role is used to grant the
-                [cloudkms.cryptoKeys.get permission](https://cloud.google.com/kms/docs/reference/permissions-and-roles#predefined).
     *   **Cloud KMS CryptoKey Encrypter/Decrypter**
         *   This is needed so that the service account can use keys stored in
             Cloud KMS to