[apisix-ingress-controller] Support custom ServiceAccount

Hi team,

I noticed that the apisix-ingress-controller Helm chart currently hardcodes the ServiceAccount name to .Release.Name with no option to bring your own or customise it.
Is there a reason, if not can i create a pull request?

Regards,
Phanindra

Start by inspecting the apisix-ingress-controller Helm chart's ServiceAccount template and values; the issue names no specific file or test. Confirm how the name is derived from .Release.Name, then verify rendered output with a custom ServiceAccount name and that the existing default remains unchanged.

Written by the indexing model from the issue text.