Add useUpsert operation

[kachar]

While supabase gives devs the opportunity to do insert or update with a single command, this feature doesn't seem supported by react-supabase lib

https://supabase.io/docs/reference/javascript/upsert

const { data, error } = await supabase.from('messages').upsert({
  id: 3,
  message: 'foo',
  username: 'supabot'
})

My suggestion is to include it as useUpsert hook

const [{ count, data, error, fetching }, execute] = useUpsert('messages')

async function onClickUpsert(id, message, username) {
  const { count, data, error } = await execute({
    id,
    message,
    username,
  })
}

[tmm]

Great idea. It should be easy to add. Feel free to open a pull request or I'll add to my list.

[kachar]

@tmm Added a PR for the given functionality at #6