refactor: Make docker pacakge an internal package of cmd/base

The docker package and its StartDbInDocker function should only be used
by the `boundary dev` command now. So moving it into an internal package
of `base` will prevent it from being use for tests accidentally, while
still allowing it to be used for `boundary dev`.

internal/cmd/base/dev.go

@@ -10,9 +10,9 @@ import (
 	"strings"
 
 	"github.com/hashicorp/boundary/internal/auth/oidc"
+	"github.com/hashicorp/boundary/internal/cmd/base/internal/docker"
 	"github.com/hashicorp/boundary/internal/db"
 	"github.com/hashicorp/boundary/internal/db/schema"
-	"github.com/hashicorp/boundary/internal/docker"
 	"github.com/hashicorp/boundary/internal/iam"
 	"github.com/hashicorp/boundary/internal/kms"
 	"github.com/hashicorp/boundary/internal/observability/event"