feat(grafana-cli): allow configuring admin ID for reset-admin-password (#60603)

* feat(grafana-cli): add a flag to control the admin user's ID for reset-admin-password

Since this is now more permissive, I've also added validation that the requested user is an admin.

* slight refactor to support testing

pkg/cmd/grafana-cli/commands/reset_password_command_test.go

@@ -0,0 +1,54 @@
+package commands
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/grafana/grafana/pkg/services/user"
+	"github.com/grafana/grafana/pkg/services/user/usertest"
+)
+
+func TestResetPassword(t *testing.T) {
+	tests := map[string]struct {
+		UserID    int64
+		IsAdmin   bool
+		ExpectErr error
+	}{
+		"basic success": {
+			DefaultAdminUserId,
+			true,
+			nil,
+		},
+		"default user is not an admin": {
+			DefaultAdminUserId,
+			false,
+			ErrMustBeAdmin,
+		},
+		"random user is not an admin": {
+			11,
+			false,
+			ErrMustBeAdmin,
+		},
+		"random user is an admin": {
+			11,
+			true,
+			nil,
+		},
+	}
+
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			svc := &usertest.FakeUserService{}
+			svc.ExpectedUser = &user.User{
+				IsAdmin: test.IsAdmin,
+			}
+			err := resetPassword(test.UserID, "s00pers3cure!", svc)
+			if test.ExpectErr != nil {
+				require.EqualError(t, err, test.ExpectErr.Error())
+			} else {
+				require.NoError(t, err)
+			}
+		})
+	}
+}