Support /getSamples endpoint for image servers

[JosiahParry]

Documentation: https://developers.arcgis.com/rest/services-reference/enterprise/get-samples.htm
Work against landsat: https://landsat2.arcgis.com/arcgis/rest/services/Landsat/MS/ImageServer/getSamples

#' Get Samples from Image Service
#' 
get_samples <- function(
    x,
    geometry,
    interpolation = c("bilinear", "cubic", "majority", "nearestneighbor")
    fields = NULL,
    sample_distance = NULL,
    sample_count = NULL,
    mosaic_rule = NULL,
    slice_id = NULL
) {
  
  # verify it is an image server
  check_inherits_any(x, "ImageServer")
  
  # mosaic rules: 
  # https://developers.arcgis.com/rest/services-reference/enterprise/mosaic-rules.htm
  
  # interpolation values
  # RSP_BilinearInterpolation | RSP_CubicConvolution | RSP_Majority | RSP_NearestNeighbor
  
  # TODO handle fields
  
  # prepare geometry for adding to the request. 
  # we will use prepare_spatial_filter() 
  # but the predicate is irrelevant here we will extract 
  # only the geometryType and the geometry
  geom_prepped <- prepare_spatial_filter(geometry, predicate = "intersects")
  
  b_req <- httr2::req_url_path_append(
    httr2::request(x[["url"]]),
    "getSamples"
  )
  
  resp <- httr2::req_body_form(
    b_req,
    geometryType = geom_prepped[["geometryType"]],
    geometry = geom_prepped[["geometry"]],
    outFields = "*",
    f = "json"
  )
}