pkg/helm: new watch file option to support watching dependent resources

[joelanford]

Description of the change:

• Adds a new option to the watches.yaml file called watchDependentResources, which enables users to configure whether resources defined by Helm releases are watched for reconciliation. This option is enabled by default. This is the same mechanism as the ansible-operator to maintain consistency.
• Decouples the loading of the watch file from the creation of manager factories by refactoring the loading of the watch file into a separate watches package. This makes it easier to add new watch configurations that are outside the scope of the release manager factory.
• Removes helpers that allowed watches to be configured from environment variables. Now that multiple watches are supported and new watch-specific configurations are being added, loading from the environment does not provide the necessary flexibility.

Motivation for the change:
See #885 (comment).

[joelanford]

Chatting with @robszumski, I realized there's still value in the helm-app-operator-kit UX that made it really easy to build an operator from a Helm chart using just environment variables and a Dockerfile.

The operator-sdk CLI doesn't currently expose a way to make use of these environment variables (which are removed in this PR), so I don't think we'll regress the UX by merging this PR (we unknowingly regressed it already).

Having said that, we need to think about how to simplify building operators from existing Helm charts. I'd propose that we go ahead with this PR as is and draft a proposal to implement Rob's ideas for making it easier to build Helm (and Ansible?) operator images with new CLI commands/flags.

EDIT: See #949 for the proposed UX improvement.

[shawn-hurley]

LGTM