Expose overview strategy into the layers configuration

[pomadchin]

Overview

This PR allows to specify the overview strategy to select on the resample / reproject operations.

Checklist

• Description of PR is in an appropriate section of the CHANGELOG and grouped with similar changes if possible

Notes

These overview strategies behave in the same (or in a similar) way GDALWarp overview strategies behave.

The following overview strategies support is added:

"auto-higher-resolution" # a default behavior 
         # tries to pick up a resolution that matches best
"base".  # always uses the layer with the best resolution for the resampling operations
"auto-n" # n is int, where n >= 0 # behaves like gdal, 
         # so if the reoslution is a bit off, it would pick up the less resolute overview for sampleing
"level-n" # n is int, where n >= 0 # n is a number of an overview we'd like to use 
          # for all layer sampling operations

Add the overview startegy definition into the ogcExamples project application.conf:

us-ned-hillshade = {
  type = "mapalgebrasourceconf"
  name = "us-ned-hillshade"
  title = "US NED Hillshade"
  resample-method = "bilinear"
  overview-strategy = "auto-0"
...

The default behaviour is

Addresses #215

[CloudNiner]

LGTM pending verification from client that switching strategies solves their issue!

[pomadchin]

@CloudNiner I need this PR to be merged in for the pointcloud tests (so the snapshot of gt server would be published), I think I'll merge it in without closing the related issues.

[CloudNiner]

👍 makes sense