Allow customization of the Statefulset

[tproenca]

I added extraVolumes, extraVolumesMounts, extraInitContainers and persistence.annotations to the helm chart.

The extraInitContainers is useful in a situation that you want to add an init-container to get the data from a backup copy for example. You can mount the volume from the volumeClaimTemplate, and copy the data there.

The extraVolumes, extraVolumesMounts can be used to mount the logs folder in a particular volume, and use a sidecar container like fluentd to send the logs elsewhere.

The persistence annotations is a good addition for clusters that don't support the storageClassName yet.

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[Crazybus]

This looks great! Thanks for adding these in :)

Could you also please adding the following:

1. Add the new values into the README
2. Add some tests for testing the templating logic. You can base it off the example for extraEnvs. Just a single test to ensure that it works correctly and has the right indentation level is enough.

[Crazybus]

As another note it also seems like you still need to sign the CLA.

[tproenca]

This looks great! Thanks for adding these in :)

Could you also please adding the following:

1. Add the new values into the README
2. Add some tests for testing the templating logic. You can base it off the example for extraEnvs. Just a single test to ensure that it works correctly and has the right indentation level is enough.

All done. I'm waiting for my company approve the CLA on my side.

[tproenca]

I signed the CLA, but the merging is still blocked.

[Crazybus]

jenkins test this please

[Crazybus]

Thanks so much for adding in the docs and testing 🥇 This is great!

[tproenca]

Np... I'm glad to contribute. :)