Include Partial Templates and Defaults In Existing Helm Chart

[ihcsim]

The current control plane's Helm chart is missing the proxy and proxy-init spec, and a default values.yaml config values file. The goal of this task is to update the existing chart to include the missing spec from a new partials chart. When this task is completed, users will be able to use helm install to install the Linkerd control plane, as if they are running linkerd install.

If possible, the existing linkerd install command should remain untouched. Changes to linkerd inject and multi-stage installation will also be deferred to another PR.

All new charts will be added to a new folder named, charts. Refer to #3099 for the targeted folder layout.

Some notes on configuration:

• The proxy and proxy-init YAML spec will be included in the control plane chart as partials (defined in the partials chart).
• The data of the linkerd-config config map will also be included in the control plane chart as partials (defined in the partials chart).
• The identity issuer secret TLS certificate and key must be provided by users. If absent, installation should fail.
• The CA trust root of the proxy injector and profile validator will be generated using Sprig's crypto package.
• A default values.yaml config values file with sane defaults will be provided. (See cli/cmd/install.go for some hard coded defaults.)
• For required variables, use the Sprig's defaults package to specify defaults. E.g., users won't necessarily know or care about the value of {{.Values.ControllerComponentLabel}}.
• Etc.

[alpeb]

The CA trust root of the proxy injector and profile validator will be generated using Sprig's crypto package.

This requires some minor refactoring of the TLS libs, so I created #3131 to track that effort.