[9.1][Automation] Update versions (#9678)

These files are used for picking the starting (pre-upgrade) or ending (post-upgrade) agent versions in upgrade integration tests.

The content is based on responses from https://www.elastic.co/api/product_versions and https://snapshots.elastic.co

The current update is generated based on the following requirements:

`.package-version`

```json
{
  "version": "9.1.4-SNAPSHOT",
  "build_id": "9.1.4-687d3d68",
  "manifest_url": "https://snapshots.elastic.co/9.1.4-687d3d68/manifest-9.1.4-SNAPSHOT.json",
  "summary_url": "https://snapshots.elastic.co/9.1.4-687d3d68/summary-9.1.4-SNAPSHOT.html",
  "core_version": "9.1.4",
  "stack_build_id": "9.1.4-687d3d68-SNAPSHOT"
}
```

`testing/integration/testdata/.upgrade-test-agent-versions.yml`

```json
{
  "UpgradeToVersion": "9.1.4",
  "CurrentMajors": 1,
  "PreviousMajors": 1,
  "PreviousMinors": 2,
  "SnapshotBranches": [
    "9.1",
    "9.0",
    "8.19",
    "7.17"
  ]
}
```

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

.package-version

@@ -1,8 +1,8 @@
 {
   "version": "9.1.4-SNAPSHOT",
-  "build_id": "9.1.4-ea51806b",
-  "manifest_url": "https://snapshots.elastic.co/9.1.4-ea51806b/manifest-9.1.4-SNAPSHOT.json",
-  "summary_url": "https://snapshots.elastic.co/9.1.4-ea51806b/summary-9.1.4-SNAPSHOT.html",
+  "build_id": "9.1.4-687d3d68",
+  "manifest_url": "https://snapshots.elastic.co/9.1.4-687d3d68/manifest-9.1.4-SNAPSHOT.json",
+  "summary_url": "https://snapshots.elastic.co/9.1.4-687d3d68/summary-9.1.4-SNAPSHOT.html",
   "core_version": "9.1.4",
-  "stack_build_id": "9.1.4-ea51806b-SNAPSHOT"
+  "stack_build_id": "9.1.4-687d3d68-SNAPSHOT"
 }

testing/integration/testdata/.upgrade-test-agent-versions.yml

@@ -7,6 +7,6 @@
 testVersions:
   - 9.0.7-SNAPSHOT
   - 9.0.6
+  - 8.19.4-SNAPSHOT
   - 8.19.3
-  - 8.19.3-SNAPSHOT
   - 7.17.30-SNAPSHOT