infra: configure mintmaker to automerge RPM security updates

MintMaker's separate Pull Requests for regular and security RPM lockfile updates create merge conflicts when the security PR is merged first.
Configure `rpmVulnerabilityAutomerge` to merge security PRs automatically, preventing future race conditions.
MintMaker will pick up the new configuration on its next run.

Signed-off-by: Shereen Haj <shajmakh@redhat.com>

Author: shajmakh

renovate.json

@@ -20,6 +20,7 @@
         "enabled": false
     },
     "pruneBranchAfterAutomerge": true,
+    "rpmVulnerabilityAutomerge": "ALL",
     "tekton": {
         "enabled": true,
         "fileMatch": [