Changes dates represented as strings to dates represented as a Date type

[bidoubiwa]

Description
In the task structure multiple fields represents dates but are typed as strings. It would be an improvement to change these dates to a Date type object and not a string,

Example can be found here:

meilisearch-swift/Sources/MeiliSearch/Model/Task.swift

Line 34 in ae7ad35

public let processedAt: String?

Currently the decoder is not able to transform the returned date format by Meilisearch into a Date object in swift. See error:

▿ Swift.DecodingError.dataCorrupted
  ▿ dataCorrupted: Swift.DecodingError.Context
    ▿ codingPath: 1 element
      - CodingKeys(stringValue: "duration", intValue: nil)
    - debugDescription: "Date string does not match format expected by formatter."
    - underlyingError: nil

Meilisearch is returned date the following way:

   "enqueuedAt": "2021-08-10T14:29:17.000000Z",

Which per the specs is described like this (for example with enqueuedAt):

| enqueuedAt | string | Represent the date and time as `ISO-8601` format when the task has been enqueued |

[brunoocasali]

I had a similar problem when upgrading the dart SDK: https://github.com/meilisearch/meilisearch-dart/blob/main/lib/src/client_impl.dart#L160 so I had to make a workaround in order to be able to serialize it.
Not sure if helps 👯

[bidoubiwa]

For the moment there are two API in swift. One called Date that has a ISO8601Format(_:) method but only compatible with MacOS 12+
The other is called DateFormatter and I believe with this API it is easy