[Feature] Support depth metrics

[Ben-Louis]

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Motivation

Please describe the motivation of this PR and the goal you want to achieve through this PR.

Support metrics for the depth estimation task, including RMSE, ABSRel, and etc.

Modification

Please briefly describe what modification is made in this PR.

BC-breaking (Optional)

Does the modification introduce changes that break the backward-compatibility of the downstream repos?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

Using the following configuration to compute depth metrics on NYU

dataset_type = 'NYUDataset'
data_root = 'data/nyu'

test_pipeline = [
    dict(type='LoadImageFromFile'),
    dict(dict(type='LoadDepthAnnotation', depth_rescale_factor=1e-3)),
    dict(
        type='PackSegInputs',
        meta_keys=('img_path', 'depth_map_path', 'ori_shape', 'img_shape',
                   'pad_shape', 'scale_factor', 'flip', 'flip_direction',
                   'category_id'))
]

val_dataloader = dict(
    batch_size=1,
    num_workers=4,
    persistent_workers=True,
    sampler=dict(type='DefaultSampler', shuffle=False),
    dataset=dict(
        type=dataset_type,
        data_root=data_root,
        test_mode=True,
        data_prefix=dict(
            img_path='images/test', depth_map_path='annotations/test'),
        pipeline=test_pipeline))
test_dataloader = val_dataloader

val_evaluator = dict(type='DepthMetric', max_depth_eval=10.0, crop_type='nyu')
test_evaluator = val_evaluator

Example log:

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMDet3D.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[xiexinch]

Might list optional values

[xiexinch]

Might add a ref link.