Sidecar container spec for druid

[cintoSunny]

Fixes https://github.com/druid-io/druid-operator/issues/275

Description

Currently, the Druid operator does not allow the addition of a sidecar container to Druid deployments. The only way is to inject sidecars by mutation webhooks like istio. But many orgs may not allow setting up istio or it could be an additional effort to add them.

The sidecar containers can be added like below:

sidecarContainer:
- configs:
    imageName: docker.com/ns/samplesimage:latest
    containerName: sidecar
    command: /bin/start.sh
    pullPolicy: Always
...

This PR has:

• [x] been tested on a real K8S cluster to ensure creation of a sidecar container.
• [x] been tested for backward compatibility on a real K*S cluster by applying the changes introduced here on an existing Druid cluster. If there are any backward incompatible changes then they have been noted in the PR description.
• [ ] added documentation for new or modified features or behaviors.

---

Key changed/added files in this PR

• handler.go
• druid_types.go
• handler_test.go
• broker-statefulset-sidecar.yaml
• druid-test-cr-sidecar.yaml
• druid.apache.org_druids.yaml

[AdheipSingh]

@nishantmonu51 kindly approve to run CI checks

[AdheipSingh]

@cintoSunny can you add a documentation around adding this feature, would be really helpful :) and an example spec here https://github.com/druid-io/druid-operator/blob/master/docs/examples.md

[cintoSunny]

@cintoSunny can you add a documentation around adding this feature, would be really helpful :) and an example spec here https://github.com/druid-io/druid-operator/blob/master/docs/examples.md

I have added a sample spec to example.md. Let me know what you think.

I have added documentation to features.md. Let me know what you think

[AdheipSingh]

I have tested this locally, its backward compatible. works with updated CRD. LGTM

Can you add a working example, in examples folder. It would be easier for users to test. I had to construct own yaml for test. ( the yamls in testdata wont work against the updated CRD, need to update thise. )

[cintoSunny]

I have tested this locally, its backward compatible. works with updated CRD. LGTM

Can you add a working example, in examples folder. It would be easier for users to test. I had to construct own yaml for test. ( the yamls in testdata wont work against the updated CRD, need to update thise. )

Sorry about that. I had to remove some company-specific things, hence left out a few parts. I changed it to your working example.