Persist initial value in useSessionStorage and useLocalStorage

[stoyle]

We'd like to use the storage hooks to handle random values, e.g. a generated UUID.

However the hooks do not persist the initial value. Hence reloading the hook results in a new value.

Suggestion is to add an option, .e.g persistInitialValue, defaulting to false, which does this.

Happy to contribute some code if you think this is a good idea.