use `bottlerocket-variant` crate to set up logdog conf for variants

[etungsten]

we could potentially use our new bottlerocket-variant crate to set up a ladder of different configs, ordered from most to least specific, and pick the first one that existed.

That would let us avoid at least this one symlink chore.

Originally posted by @bcressey in https://github.com/bottlerocket-os/bottlerocket/pull/2140#discussion_r891316822