support the RSDD dataset

[SAR-Images-Understanding-Yang]

add the config rsdd and rsdd dataset README.md

Thanks for your contribution and we appreciate it a lot. The following instructions would make your pull request more healthy and more easily get feedback. If you do not understand some items, don't worry, just make the pull request and seek help from maintainers.

Motivation

Rotated object for SAR images is my research interest, so i convert the annotation of RSDD dataset to the 4 point annotation, so that i can do my experiments using mmrotate.

Modification

RSDDDataset will be added and a RSDDdataset readme will be added to the tools/data/RSDD, because i converted the annotation of RSDD dataset to the 4 point annotation, so that i can do my experiments using mmrotate directly.

BC-breaking (Optional)

Does the modification introduce changes that break the back-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)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

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. The documentation has been modified accordingly, like docstring or example tutorials.

[yangxue0827]

Thanks for your contribution. Please follow https://github.com/open-mmlab/mmcv/blob/master/CONTRIBUTING.md to set pre-commit hook and fix the lint error. It is best to provide a configuration file that works on this dataset like https://github.com/open-mmlab/mmrotate/blob/main/configs/kld/rotated_retinanet_hbb_kld_stable_r50_fpn_6x_hrsc_rr_oc.py.

[OpenMMLab-Assistant-004]

Hi @TommyYangXP ！We are grateful for your efforts in helping improve mmrotate open-source project during your personal time.

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Thank you again for your contribution❤

[CLAassistant]

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