teleport-kube-agent Helm chart: Optional overwrite of .Release.Name

[eric-as]

This PRs enables to overwrite the .Release.Name if needed, for example to install multiple instances of teleport-kube-agent into the same cluster or even namespace.
If the value for the key releaseNameOverwrite (introducted in this PR) ist not set, this should be a NOOP.

[github-actions]

Thank you for your submission, we really appreciate it. Like many open-source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution. You can sign the CLA by just posting a Pull Request Comment same as the below format.

---

I have read the CLA Document and I hereby sign the CLA

---

_{You can retrigger this bot by commenting recheck in this Pull Request. Posted by the CLA Assistant Lite bot.}