feat(manifests): add name on workflow-controller-metrics service port

[dustinspecker]

While adding a name is optional from a Kubernetes standpoint since there
is only one port listed, the named port makes using Prometheus easier.
There's a targetPort option for Prometheus' ServiceMonitor Custom
Resource, but this targetPort doesn't relate to the service's
targetPort, but in fact the containers' targetPort pointed at by the
service [1]. And since the workflow-controller deployment doesn't
actually explicitly list the ports the targetPort configuration on a
ServiceMonitor does nothing. So having the named port on the service's
port makes it much easier to use for Prometheus.

1 - prometheus-operator/prometheus-operator#2515

I'm not actually sure how to use this service with Prometheus-operator without this named port. I considered this commit a feature, but might actually be a fix. Please let me know if it's preferred for me to use fix instead of feat for this.

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this is a chore.
• The title of the PR is (a) conventional, (b) states what changed, and (c) suffixes the related issues number. E.g. "fix(controller): Updates such and such. Fixes #1234".
• I've signed the CLA.
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My builds are green. Try syncing with master if they are not.
• My organization is added to USERS.md.