[artifactory-ha] Add option to set Environment Variables option to filebeat sidecar

[stokkie90]

PR Checklist

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

• [x] Chart Version bumped
• [x] CHANGELOG.md updated
• [x] Variables and other changes are documented in the README.md
• [x] Title of the PR starts with chart name (e.g. [artifactory])

What this PR does / why we need it:

To Enable setting values from the Environment: https://www.elastic.co/guide/en/beats/filebeat/current/using-environ-vars.html

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

Special notes for your reviewer:

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[stokkie90]

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