Fix interface conversion during pg edit

[majst01]

cloudctl postgres edit ade2ed7b-3bdd-4863-b234-edbdbf43a89c
panic: interface conversion: interface {} is *models.V1PostgresCreateRequest, not *models.V1PostgresUpdateRequest

goroutine 1 [running]:
github.com/fi-ts/cloudctl/cmd.readPostgresUpdateRequests.func1(0x24994e0, 0xc000724000)
	/work/cmd/postgres.go:526 +0x166
github.com/fi-ts/cloudctl/cmd/helper.ReadFrom(0xc0007ea140, 0x47, 0x24994e0, 0xc000724000, 0xc00015bb58, 0xb, 0xc)
	/work/cmd/helper/helper.go:125 +0x1d9
github.com/fi-ts/cloudctl/cmd.readPostgresUpdateRequests(0xc0007ea140, 0x47, 0xc0000a2168, 0x0, 0x0, 0x0, 0x0)
	/work/cmd/postgres.go:525 +0xa5
github.com/fi-ts/cloudctl/cmd.postgresEdit.func2(0xc0007ea140, 0x47, 0x0, 0x1)
	/work/cmd/postgres.go:504 +0x3c
github.com/fi-ts/cloudctl/cmd/helper.Edit(0x76b4937, 0x24, 0x2677a70, 0x2677a78, 0x0, 0x0)
	/work/cmd/helper/helper.go:158 +0x2ee
github.com/fi-ts/cloudctl/cmd.postgresEdit(0xc00009da50, 0x1, 0x1, 0x0, 0x0)
	/work/cmd/postgres.go:519 +0xae
github.com/fi-ts/cloudctl/cmd.glob..func45(0x3294300, 0xc00009da50, 0x1, 0x1, 0x0, 0x0)
	/work/cmd/postgres.go:89 +0x3f
github.com/spf13/cobra.(*Command).execute(0x3294300, 0xc00009da20, 0x1, 0x1, 0x3294300, 0xc00009da20)
	/go/pkg/mod/github.com/spf13/cobra@v1.1.3/command.go:852 +0x472
github.com/spf13/cobra.(*Command).ExecuteC(0x3297780, 0x60, 0x8100a68, 0x60)
	/go/pkg/mod/github.com/spf13/cobra@v1.1.3/command.go:960 +0x375
github.com/spf13/cobra.(*Command).Execute(...)
	/go/pkg/mod/github.com/spf13/cobra@v1.1.3/command.go:897
github.com/fi-ts/cloudctl/cmd.Execute()
	/work/cmd/root.go:57 +0x31
main.main()
	/work/main.go:8 +0x25