feat: make headless service configurable

[AndreasSchwalb]

Description

Add headless monitor service configurable

Checklist

• I've read the guidelines for contributing to this repository.
• [] I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).

For a better usability of the helm chart it may be useful to make the headless service configurable. This is just relevant if you want to export the metrics and scrape them with prometheus.
With this configuration flag, it is not necessary anymore to adjust the service deployment by hand.

[CLAassistant]

All committers have signed the CLA.

[chen-keinan]

@AndreasSchwalb thank you for the contribution, could you please rebase with upstream and run
mage generate:docs for updating helm docs

Please also sign the CLA

[chen-keinan]

@AndreasSchwalb LGTM 🚀 thanks you for the contribution