Add nginx-ldapauth-proxy allowing to set authorization header

[iblackman]

PR Description

Extracted from https://github.com/helm/charts/tree/master/stable/nginx-ldapauth-proxy and added an option to pass basic auth.

Checklist

• Have you reviewed and updated the chart default values if necessary?
• Have you reviewed and updated the chart documentation if necessary?
• Does your branch follow the naming convention of {chartNameWithDashes}-v{versionString}-{optionalPatchVersion}?
• Have you bumped the version in the chart's Chart.yaml?

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• Has a tag name that matches your PR branch name (see above)
• Has a description that summarizes the changes made

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