Add Support for additional deployment configuration

Thanks for starting this project. I'm currently evaluating using the operator to deploy pipelines in my organization. At this point I understand that it alpha, but I was wondering if you have any plans to add additional configuration options to the `Pipeline` resource.

I can see a clear need for the following configurable properties:
- Secrets
- Resource Requirements (limits/requests)
- Additional Labels and possibly Annotations
- env configuration via Env and/or EnvFrom
- Additional Volumes
- Additional flags for the benthos cmd if configuration is not supported via env vars

It would seem simple enough to add these and more if necessary. In fact I have already modified the controller to add: `EnvFrom`, `Resources`, `Labels`, and `Annotations` which correspond to the available configuration in the `DeploymentSpec`.

I did this only to evaluate if we could use the operator and it was very straightforward to implement. I added these properties to the root of the schema, but that was just a quick and dirty approach since it meant not having to create a new type, but rather just update the Deployment that the operator creates with the additional configuration.

I would be willing to submit PRs to help in the development effort.