builder: Please retain functionality to supply Go binary at command time

[braydonk]

Is your feature request related to a problem? Please describe.
My intended setup for a collector binary built by OCB is the following:

• Write a manifest.yaml
• Download a local copy of a Go binary at a specific version
• Use that Go binary to install a local copy of builder
• Provide the locally installed Go binary as the Go binary for builder, today using the --go flag

This flag is being deprecated in favour of the distribution::go config value. However in my desired setup, I would have to separately track within the manifest the eventual location of the Go binary that I'm going to install when it's time to build. It is logically much cleaner to simply provide the Go binary I want at command-time rather than being forced to track this in configuration.

Describe the solution you'd like
Either keep the --go flag, or provide something other mechanism to provide a Go binary at command-time like an env var.

Describe alternatives you've considered
As stated above, I could just track the location that I know the local Go binary will be installed when it is, but this is less clean than simply providing it at command-time.

[mx-psi]

Relates to #7976