Support direct annotation argument (--train/val-ann-files)

[sungmanc]

Summary

• Support direct annotation input for CoCo
  For now, we can use --train/val-ann-files argument

• Support unlabeled file list argument

• Add unit-tests for both functionalities

• Unifying the data_root + data_roots --> data_roots

• Edit the CHANGELOG

• Edit the documents
  

• Add unlabeled example assets

• Add subset annotation example assets

How to test

[To check the direct annotation functionality (Dataset Adapter)]
[To check the unlabeled file functionality]

• tox -e pre-merge-all-py310 -- tests/unit/core/data/adapter/test_init.py

[To check the direct annotation functionality (Datumaro function itself)]

• tox -e pre-merge-all-py310 -- tests/unit/core/data/manager/test_dataset_manager.py

Checklist

• I submit my changes into the develop branch
• I have added description of my changes into CHANGELOG
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below)

# Copyright (C) 2023 Intel Corporation
#
# SPDX-License-Identifier: MIT

[yunchu]

please add label for this PR.

[harimkang]

LGTM!

[cih9088]

I noticed that --{subset}--data-roots and --{subset}-ann-files arguments have descriptions saying one can pass comma separated list of paths but it certainly does not support it.

It would be better to rename the plural to singular and modify the description or implement the comma separated list of paths feature.

[sungmanc]

I noticed that --{subset}--data-roots and --{subset}-ann-files arguments have descriptions saying one can pass comma separated list of paths but it certainly does not support it.

It would be better to rename the plural to singular and modify the description or implement the comma separated list of paths feature.

Agree, then could I change all variable and description at next PR?