#256 Add support for HAProxy service externalIPs

[amfleurke]

• add new haproxy.service.externalIPs and 2 bugfixes in README:
• fix haproxy.image.serviceAccountName to haproxy.serviceAccountName
• add missing haproxy.service.loadBalancerIP entry

What this PR does / why we need it:

I need to deploy the HAProxy service as type LoadBalancer with a specified IP address using externalIPs field. This field is not supported yet

Which issue this PR fixes

• fixes # #256

Special notes for your reviewer:

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• [X] DCO signed
• [X] Chart Version bumped
• [X] Variables are documented in the README.md
• [X] Title of the PR starts with chart name (e.g. [stable/mychartname])