Adds missing variable to deploy-autoscaler script

[bonzofenix]

Adds missing environment variable to fix issue on concourse pipeline:

broken job: https://concourse.app-runtime-interfaces.ci.cloudfoundry.org/teams/app-autoscaler/pipelines/app-autoscaler-release/jobs/acceptance-log-cache-syslog-cf/builds/10

job with fix: https://concourse.app-runtime-interfaces.ci.cloudfoundry.org/teams/app-autoscaler/pipelines/app-autoscaler-release-fix-missing-metricsforwarder-host-variable/jobs/acceptance-log-cache-syslog-cf/builds/1

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
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