Please add a "boundary_target_host_source" to be able to define host sources for an existing target.

Use case

Having two different terraform repository : One to define all infra resources of a project and one to define all project resources.

Infra resources includes for example a boundary target for the database without the address because the database address doesn't exist yet at this stage.

Project resources includes the DNS of the database in a dedicated boundary host source, which is known at this stage because database is a project resource and which change on each redeployments.

This would allow us to define fine tuned permission grants on targets on infra side while being able to define target addresses dynamically on project sides.