[addons] Changed addon helm config format to native HCL data object

[jrsdav]

This is a mostly cosmetic change where we're standardizing on how we pass values to helm_release. Other changes are detailed below.

Previously this was done through a number of set {} value blocks, which is pretty rigid in terms of data types (lists, for instance, require some ugly hacks in HCL).

The better approach that we've found is to define a complex type, and pass that to the values = [] input with yamlencode(). We'll continue this pattern in other modules and make it the standard going forward.

Other changes in this PR include:

• Updated default Kubernetes version for EKS from 1.18 to 1.20
• Chart version defaults for minor updates
• Creates a Calico CR when the Tigera operator is enabled and installed

[jrsdav]

Enabling the calico CR introduces some network connectivity problems on workloads within the cluster.

It's still undetermined if we will be using Calico for advanced network policies now that we're using Istio.

I have disabled Calico installing by default for the time being until this can be addressed.