cli: Add list-datasets command

Add simple command to print the names of the Software Heritage graph datasets that can be downloaded with the following command:

$ swh graph download --name <dataset_name> <target_directory>

$ swh graph list-datasets -h
Usage: swh graph list-datasets [OPTIONS]

  List graph datasets available for download.

  Print the names of the Software Heritage graph datasets that can be
  downloaded with the following command:

  $ swh graph download --name <dataset_name> <target_directory>

Options:
  --s3-bucket TEXT  S3 bucket name containing Software Heritage graph
                    datasets. Defaults to 'sotwareheritage'
  -h, --help        Show this message and exit.

$ swh graph list-datasets 
2018-09-25
2020-05-20
2020-12-15
2021-03-23-cpython-3-5
2021-03-23-popular-3k-python
2021-03-23
2022-04-25
2022-12-07-history-hosting
2022-12-07
2023-09-06-history-hosting
2023-09-06-popular-1k
2023-09-06
2024-05-16-history-hosting
2024-05-16-sux
2024-05-16
2024-08-23-popular-500-python
2024-08-23
2024-08-23_popular-4-shell

Jenkins job DGRPH/gitlab-builds #2496 succeeded in 47 min.
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approved this merge request

added 2 commits

• 683a7ac6 - 1 commit from branch swh/devel:master
• a459fb03 - cli: Add list-datasets command

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Jenkins job DGRPH/gitlab-builds #2501 succeeded in 21 min.
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merged manually