Add endpoint to return availability per day

[bitscraps]

On the new BBF we need to present a list of days with activities or rentals available. Also we need to return a list of rentals/activities available on a day.

This may currently be got via multiple queries and parsing of data. However to simplify things we want to propose an endpoint which returns combined data for activities and rentals in a flatter format than we currently have, broken down by day rather than by individual time slots. With the resource units highlighting the max available at some point that day. This will take a start time, finish time allowing us to use it for the calendar view where we query for the month and the table listing products which will be for 1 day.

{
  [
    {
       schedulable {
        id
      },
      date: '2022-02-01',
      resource_units: {
       id: '123',
      available: 1
     } 
  ]
}