Dockerfile.agent: align runtime stage USER with manager Dockerfile

[juliakreger]

Add USER_ID ARG defaulting to 65532 and set USER in the runtime stage, consistent with how the manager Dockerfile configures its runtime user.

[openshift-ci]

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[centosinfra-prod-github-app]

Build failed (check pipeline). Post recheck (without leading slash)
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https://gateway-cloud-softwarefactory.apps.ocp.cloud.ci.centos.org/zuul/t/rdoproject.org/buildset/5165fcc896e64c29b384284842018984

✔️ openstack-baremetal-operator-content-provider SUCCESS in 40m 22s
❌ openstack-baremetal-operator-crc-podified-edpm-baremetal NODE_FAILURE Node(set) request 099-0000172631 failed in 0s
❌ openstack-baremetal-operator-edpm-baremetal-minor-update NODE_FAILURE Node(set) request 099-0000172632 failed in 0s

[juliakreger]

recheck

[centosinfra-prod-github-app]

Build failed (check pipeline). Post recheck (without leading slash)
to rerun all jobs. Make sure the failure cause has been resolved before
you rerun jobs.

https://gateway-cloud-softwarefactory.apps.ocp.cloud.ci.centos.org/zuul/t/rdoproject.org/buildset/19216abb9cfa47e8ba4ffd3c1b8c4852

✔️ openstack-baremetal-operator-content-provider SUCCESS in 59m 31s
❌ openstack-baremetal-operator-crc-podified-edpm-baremetal NODE_FAILURE Node(set) request 099-0000173663 failed in 0s
❌ openstack-baremetal-operator-edpm-baremetal-minor-update NODE_FAILURE Node(set) request 099-0000173664 failed in 0s

[juliakreger]

recheck

[centosinfra-prod-github-app]

Build failed (check pipeline). Post recheck (without leading slash)
to rerun all jobs. Make sure the failure cause has been resolved before
you rerun jobs.

https://gateway-cloud-softwarefactory.apps.ocp.cloud.ci.centos.org/zuul/t/rdoproject.org/buildset/f2228b4b4a074fe293acba09fc6d7b99

✔️ openstack-baremetal-operator-content-provider SUCCESS in 22m 17s
❌ openstack-baremetal-operator-crc-podified-edpm-baremetal NODE_FAILURE Node(set) request 099-0000176612 failed in 0s
❌ openstack-baremetal-operator-edpm-baremetal-minor-update NODE_FAILURE Node(set) request 099-0000176613 failed in 0s