[graphite] add loadBalancerIP attribute

[nbouron]

What this PR does / why we need it:

In some cases we need to set the loadBalancerIP with a preprovisioned IP in case of a service of type LoadBalancer, this is why i created this PR.

Special notes for your reviewer:

Thank's for your work ! :heart:

Checklist

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

• [ x] DCO signed
• [ x] Chart Version bumped (if the pr is an update to an existing chart)
• [ x] Variables are documented in the README.md
• [ x] Title of the PR starts with chart name (e.g. [fluentd-elasticsearch])