[graphite] Add securityContext as parameter

[claudio-walser]

Signed-off-by: Claudio Walser [email protected]

What this PR does / why we need it:

It allows to pass the pods securityContext as a parameter for the graphite charts

Which issue this PR fixes

Does not exactly fix an issue. It was reported, but on a different chart: https://github.com/kiwigrid/helm-charts/issues/212 I do have the same issue on the graphite chart

Checklist

• [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])