Address support export Kuttl test race condition

Adds a Kuttl assert to verify that the initial pgBackRest backup
has completed before moving on to the first support export archive
content test. This is required because slowness in certain
environments resulted in unnexpected archive content for the
process gathering steps.

Issue: [sc-18017]

Author: tjmoore4

testing/kuttl/e2e/support-export/00-assert.yaml

@@ -29,3 +29,13 @@ status:
       readyReplicas: 1
       replicas: 1
       updatedReplicas: 1
+  pgbackrest:
+    repoHost:
+      apiVersion: apps/v1
+      kind: StatefulSet
+      ready: true
+    repos:
+    - bound: true
+      name: repo1
+      replicaCreateBackupComplete: true
+      stanzaCreated: true