Add GLPN
# What does this PR do?

This PR implements [GLPN](https://arxiv.org/abs/2201.07436), Global Local Path Networks, for state-of-the-art depth estimation (number 2 on paperswithcode for KITTI and NYUv2 benchmarks).

To do:

- [x] transfer weights to author's username
- [x] add tests for GLPNFeatureExtractor
- [x] rename `in_index` to something better
- [x] define `DepthEstimatorOutput`
_The documentation is not available anymore as the PR was closed or merged._<|||||>Ok I've addressed all comments. Waiting for the author to respond such that I can transfer the weights to his name.