Fixes https://github.com/apache/pulsar-helm-chart/issues/250
### Motivation
`httpNumThreads` is hardcoded to 8 in `charts/pulsar/templates/proxy-configmap.yaml`
When trying to override in `values.yaml` by using `proxy.configData.httpNumThreads` we get an error because the keys get duplicated.
This happens because `{{ toYaml .Values.proxy.configData | indent 2 }}` doesn't deduplicate the keys and there is no other way to set `httpNumThreads`
### Modifications
Removing the key from charts/pulsar/templates/proxy-configmap.yaml and adding it to the values yaml solves the problem.
### Verifying this change
- [x] Make sure that the change passes the CI checks.
c05f659ff4