Consume LDFLAGS in Makefile

[agouin]

Context and purpose of the change

For static builds with CGO_ENABLED, we need to pass LDFLAGS='-linkmode external -extldflags "-static"'. This allows us to build a single statically linked binary for use in our heighliner docker images

Brief Changelog

Consume LDFLAGS env var and pass to go build -ldflags

Author's Checklist

This change is a trivial rework / code cleanup without any test coverage

Reviewers Checklist

All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.

I have...

• reviewed state machine logic
• reviewed API design and naming
• manually tested (if applicable)
• confirmed the author wrote unit tests for new logic
• reviewed documentation exists and is accurate

Documentation and Release Note

• Not documented because there are no changes to the documented build process. Documentation could be added later for static binary builds, but probably unnecessary.

[asalzmann]

@agouin you should be good to merge now! the labeler action has a bug that prevents it from working properly on forks, so I removed the requirement from the branch

[agouin]

Thank you!