Add post_process_depth_estimation to image processors and support ZoeDepth's inference intricacies (#32550)

* add colorize_depth and matplotlib availability check

* add post_process_depth_estimation for zoedepth + tests

* add post_process_depth_estimation for DPT + tests

* add post_process_depth_estimation in DepthEstimationPipeline & special case for zoedepth

* run `make fixup`

* fix import related error on tests

* fix more import related errors on test

* forgot some `torch` calls in declerations

* remove `torch` call in zoedepth tests that caused error

* updated docs for depth estimation

* small fix for `colorize` input/output types

* remove `colorize_depth`, fix various names, remove matplotlib dependency

* fix formatting

* run fixup

* different images for test

* update examples in `forward` functions

* fixed broken links

* fix output types for docs

* possible format fix inside `<Tip>`

* Readability related updates

Co-authored-by: Pavel Iakubovskii <qubvel@gmail.com>

* Readability related update

* cleanup after merge

* refactor `post_process_depth_estimation` to return dict; simplify ZoeDepth's `post_process_depth_estimation`

* rewrite dict merging to support python 3.8

---------

Co-authored-by: Pavel Iakubovskii <qubvel@gmail.com>

tests/pipelines/test_pipelines_depth_estimation.py

@@ -129,7 +129,7 @@ class DepthEstimationPipelineTests(unittest.TestCase):
 
         # This seems flaky.
         # self.assertEqual(outputs["depth"], "1a39394e282e9f3b0741a90b9f108977")
-        self.assertEqual(nested_simplify(outputs["predicted_depth"].max().item()), 29.304)
+        self.assertEqual(nested_simplify(outputs["predicted_depth"].max().item()), 29.306)
         self.assertEqual(nested_simplify(outputs["predicted_depth"].min().item()), 2.662)
 
     @require_torch