chore(vdev): extract vector-vrl-doc-builder into unpublished crate

[thomasqueirozb]

Summary

Moves the build vector-vrl-docs command out of vdev and into a new publish = false workspace crate (lib/vector-vrl/doc-builder). This removes the path dependency on vector-vrl-functions (and vrl/docs) from vdev, unblocking cargo publish for the vdev crate.

The Makefile target generate-vector-vrl-docs is updated to invoke cargo run -p vector-vrl-doc-builder directly.

Vector configuration

NA

How did you test this PR?

NA

Change Type

• Bug fix
• New feature
• Dependencies
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

References

NA