lakefs superuser command crash with nil access

[nopcoder]

The superuser command crash with nil access pointer.

$ lakefs superuser --user-name admin

Fails with the following:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x48 pc=0x1032fe60c]

goroutine 1 [running]:
github.com/treeverse/lakefs/pkg/auth.NewDBAuthService({0x1043a3730, 0x1400016bcd0}, {0x1043708d8, 0x140000e56c8}, {0x1, 0x400, 0x4a817c800, 0xb2d05e00}, {0x0, 0x0})
	/Users/barak/work/lakeFS/pkg/auth/service.go:234 +0x4c
github.com/treeverse/lakefs/cmd/lakefs/cmd.glob..func10(0x104f49e40, {0x140004fa060, 0x0, 0x2})
	/Users/barak/work/lakeFS/cmd/lakefs/cmd/superuser.go:45 +0x420
github.com/spf13/cobra.(*Command).execute(0x104f49e40, {0x140004fa040, 0x2, 0x2})
	/Users/barak/go/pkg/mod/github.com/spf13/cobra@v1.4.0/command.go:860 +0x640
github.com/spf13/cobra.(*Command).ExecuteC(0x104f4a340)
	/Users/barak/go/pkg/mod/github.com/spf13/cobra@v1.4.0/command.go:974 +0x410
github.com/spf13/cobra.(*Command).Execute(...)
	/Users/barak/go/pkg/mod/github.com/spf13/cobra@v1.4.0/command.go:902
github.com/treeverse/lakefs/cmd/lakefs/cmd.Execute()
	/Users/barak/work/lakeFS/cmd/lakefs/cmd/root.go:33 +0x30
main.main()
	/Users/barak/work/lakeFS/cmd/lakefs/main.go:6 +0x20

Relevant to v0.64.0, v0.65.0, v0.66.0 and v0.67.0