Add possibility to run sidecars with vault

[shahbazn]

Problem: This chart does not allow running sidecar containers with vault, that might me needed for some scenarios e.g. running prometheus exporter.

Solution: Add configurable sidecar containers to the chart

[hashicorp-cla]

All committers have signed the CLA.

[ncabatoff]

You shouldn't need a prometheus exporter now that prometheus metrics can be scraped directly from Vault.

[shahbazn]

@ncabatoff agreed running an exporter is not necessary now that the metrics api can be scrapped directly, but might still be enough for some users to run an exporter which only polls the health api and already works with existing grafana dashboards.

Could there be other cases of running auxiliary services with vault?

[ncabatoff]

Could there be other cases of running auxiliary services with vault?

Sure, I wasn't suggesting the PR should be rejected, I was just letting you know in case you weren't aware that a prometheus exporter isn't strictly necessary.

[jasonodonnell]

Hi @shahbazn, you'll need to sign the CLA for us to consider this PR. Additionally can you add unit tests for this configurable? You can find the existing tests under test/unit. Thanks!

[shahbazn]

Hi @jasonodonnell I have added the unit tests now. Had to force push the initial commits to include my email address for CLA to work.

[shahbazn]

Hi @jasonodonnell the PR is ready to be reviewed.

[AnthonyHerman]

FWIW I'm using this already. Works great.

[jasonodonnell]

LGTM, thanks!

[jasonodonnell]

Hi @shahbazn, upon further review there's an error in your test code. You are missing a closing brace on server/standalone-StatefulSet: no extra containers added. This will need to be fixed prior to merging.

[iusergii]

This can be solution for #109.

[jasonodonnell]

LGTM, thanks @shahbazn !