POST request support for search method

[hatched-VitaliyYatsunyk]

Currently search Algolia method assumes and supports only GET requests to Algolia REST API.
We faced a problem when sending very long lists of arguments (filters, facetFilters, etc) because of the max request URL length.

In order to resolve this I added support for POST request type which can be specified as follows:

# assuming options variable can have some other arguments, like paging for example

option = options |> Enum.concat([request_method: :post])
...
case Algolia.search(index_name, query, options) do
    {:ok, results} ->
        ...
    {:error, _, message}   ->
        {:error, message}
    {:error, message}      ->
        {:error, message}
end