Fix the docker_target parameter for toolchains

[pbecotte]

We have to update the configure parameter to actually use docker_target. Once that is setup, we have to make sure that the executable is added to the runfiles, and update the entrypoint script to find the built binary. This should resolve #2170

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Issue Number: #2170

What is the new behavior?

Fixes the functionality to work as described

Does this PR introduce a breaking change?

• Yes
• No

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