ingest GNU Savannah Git repositories

GNU Savannah has a CGit interface at https://git.savannah.gnu.org/cgit/ We should ingest all Git repositories listed there.

|--------+---------------------------------------------+-----------------------------------+----------------+----------------+----------------|
| status | url                                         | url-prefix                        | instance       | # repos listed | # origins      |
|--------+---------------------------------------------+-----------------------------------+----------------+----------------+----------------|
| done   | http://git.savannah.gnu.org/cgit/           | http://git.savannah.gnu.org/git/  | gnu-savannah   |           1021 |           1021 |
|--------+---------------------------------------------+-----------------------------------+----------------+----------------+----------------|

Thanks Mohammad Akhlaghi for the heads up

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Migrated from T1451 (view on Phabricator)