Make version and URL of downloaded imgpkg binary configurable in Build Tooling For Integrations

[codegold79]

Background Information

Currently, the Carvel imgpkg tool is used by Build Tooling for Integrations to build and publish both controllers and Tanzu CLI plugins.

The imgpkg URL for package-tools (for building and publishing controllers) is stored in a config file located in package-tools/cmd/config/carvel-tools-config.yaml:

url: https://github.com/vmware-tanzu/carvel-imgpkg/releases/download/{{ .VERSION }}/imgpkg-{{ .OS }}-{{ .ARCH }} 

The imgpkg URL for plugins is stored in templates/Dockerfile:

then wget -O /bin/imgpkg https://github.com/vmware-tanzu/carvel-imgpkg/releases/download/${IMGPKG_VERSION}/imgpkg-linux-${TARGETARCH} && \ 

At one point (code was not merged), the imgpkg version for plugins was retrieved via a config file that was not always reachable:

IMGPKG_VERSION ?= $(shell awk 'BEGIN{ RS="- " }{ if( $$2=="imgpkg" ){ print $$4 } }' ../../package-tools/cmd/config/carvel-tools-config.yaml)

This issue was created in response to a few feedback comments from @sathyanarays and @avi-08 for a pull request:

• Plugin builder compile and publish in docker stages #59 (comment)
• Plugin builder compile and publish in docker stages #59 (comment)

Feature Description:

Build Tooling for Integrations should get the Carvel imgpkg version and URL using a common pathway or a common place.

Expected Outcome:

• The URL and version should be configurable by the end user.
• Enable end users to download the Carvel imgpkg binary from a private, internal location, and not from the public internet.
• The URL and versions used by package-tools and building/publishing Tanzu CLI plugins should by default be the same. According to @yharish991, divergent imgpkg versions may cause problems.