Make local registry and nginx optional

[ptrivedi]

This change makes registry certificate hosting URL and tink-worker image name:tag configurable.
It also adds a check for whether registry certificate is required and allow for absolute URIs
to be specified for action images in workflow template.

• If you are using a registry with a self-signed certificate, you can specify
  a custom URL of where the certificate is hosted. On boots, use extra-kernel-args
  command-line parameter to specify a kernel argument with key 'registry_cert_url'
  and value set to the URL location for registry CA certificate. Boots will pass this
  as a kernel command-line parameter to Hook

• In order to specify a custom absolute URI name:tag for tink-worker image instead of
  defaulting to the hardcoded default of 'tink-worker:latest', use the
  extra-kernel-args command-line parameter on Boots to specify a kernel argument with
  key 'tink_worker_image' and value set to the absolute URI of tink-worker image.
  Boots passes this to hook as a kernel command-line parameter

• If you are using a public registry with trusted CA certificate, bootkit and
  tink-docker do not need to download and setup registry certificate. Use
  extra-kernel-args command-line parameter on Boots to set a kernel parameter with
  key 'registry_cert_required' and value set to 'true' or 'false' to indicate this.
  Since we are making local registry optional, we need to make the certificate
  download and setup optional

• Currently the tink-worker code always prepends the specified docker_registry to
  the action images specified in the tinkerbell action template. The newly added
  use_absolute_action_image_uri allows specifying the full URI for the action image
  in the template and prevents the hardcoded prepending of the registry to these.
  This allows action images to potentially reside in different registries. Pass this
  kernel as the key=value kernel parameter from Boots to Hook as explained above. Value
  would be set to 'true' or 'false'

Description

Why is this needed

Fixes: #

How Has This Been Tested?

How are existing users impacted? What migration steps/scripts do we need?

Checklist:

I have:

• updated the documentation and/or roadmap (if required)
• added unit or e2e tests
• provided instructions on how to upgrade

[micahhausler]

I think certURL makes sense here, we can probably infer registryCertRequired based on the presence of certURL

[micahhausler]

I think we can drop this parameter

[micahhausler]

Can you run gofmt on this?

[jacobweinstock]

This has gone stale and i believe all of this functionality now exists. Please re-open if you feel otherwise or would like to revisit this. Thank you!