Allow setting of Monitoring CCS and Screenshotting Sandbox via env vars (#187018)

## Summary

#183795

Allow configuration of monitoring.ui.ccs.enabled and
xpack.screenshotting.browser.chromium.disableSandbox settings via
environment variables in the kibana-docker startup script within the
official Kibana Docker Image.


### Checklist

Delete any items that are not applicable to this PR.


### Risk Matrix

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### For maintainers

- [ ] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker

@@ -117,6 +117,7 @@ kibana_vars=(
     monitoring.cluster_alerts.email_notifications.email_address
     monitoring.kibana.collection.enabled
     monitoring.kibana.collection.interval
+    monitoring.ui.ccs.enabled
     monitoring.ui.container.elasticsearch.enabled
     monitoring.ui.container.logstash.enabled
     monitoring.ui.elasticsearch.hosts
@@ -362,6 +363,7 @@ kibana_vars=(
     xpack.reporting.roles.allow
     xpack.reporting.roles.enabled
     xpack.ruleRegistry.write.enabled
+    xpack.screenshotting.browser.chromium.disableSandbox
     xpack.security.accessAgreement.message
     xpack.security.audit.appender.fileName
     xpack.security.audit.appender.layout.highlight