Pagination Improvements

[pomadchin]

Describe the bug
We don't support all kinds of paginations, accroding to https://github.com/radiantearth/stac-api-spec/tree/master/item-search#pagination not only next is an acceptable pagination reference, other field names can be used.

To reproduce see https://github.com/pomadchin/stac4s/tree/fix/stac-client and the code sample below:

  describe("Integration test") {
    it("should query by bbox") {
      val filtersString =
        """
          |{
          |    "collections": ["sentinel-s2-l2a-cogs"],
          |    "datetime": "2021-06-01T19:09:23.735395Z/2021-06-30T19:09:23.735395Z",
          |    "bbox": [-92.2646, 46.6930, -92.0276, 46.9739]
          |}""".stripMargin

      val filters = parse(filtersString).flatMap(_.as[SearchFilters]).valueOr(throw _)

      val res = SttpStacClient(backend, uri"https://earth-search.aws.element84.com/v0/search")
        .search(filters)
        .take(30)
        .compile
        .toList
        .unsafeRunSync()

      println(res.length)
    }
  }