[telegraf] Add init container in telegraf chart

[sebastienrospars]

Hello,

This pull request is made in order to add optional init container in telegraf chart.

My goal is to use it to create an influx database with specified retention policy instead of create a dedicated job to do this.

Test performed
Deployed in kubernetes cluster with default values, and with simple init container (echo "OK")

• CHANGELOG.md updated
• Rebased/mergable
• Tests pass
• Sign CLA (if not already signed)

Thanks by advance

[powersj]

@wojciechka is there a way to kick of tests? Any objection to this?

[zekena2]

I made a PR that implements the same functionalitiy (and more) please check it as well it can add multiple init containers.

[sebastienrospars]

I closing my pull request, the work provided by @zekena2 is more exhaustive in this PR #523.

Thanks by advance :)