In addition to Christoph Bergs script, to import packages to salsa.debian.org, I'd like to provide some more ways to determine the namesapce_id parameter you'll need.
Say that GROUP is the name of the group or a string of the groups name and that TOKEN is a personal access token you created. So this will work much faster:
curl --request GET -d "search=GROUP" -s https://salsa.debian.org/api/v4/groups | jq '.[].id'
If the group is not public, you need to add your token:
curl [..] --header "PRIVATE-TOKEN: TOKEN" [..]
The command might provide several IDs, if the search term matches several groups. In this case, you might want to have a look at the raw output without piping it to jq or look at the result of ...
https://salsa.debian.org/api/v4/groups/?search=GROUP
... in a browser. Interestingly, the latter doesn't provide any output in the browser, if you are not part of the group. But it provides the necessary information using curl. Bug or feature?
Another way that works is, to look at the output of...
https://salsa.debian.org/api/v4/namespaces
... when you are logged in or ...
curl --request GET --header "PRIVATE-TOKEN: TOKEN" https://salsa.debian.org/api/v4/namespaces
This has the advantage of also getting the namespace_id for your personal repository, say for e.g. importing projects hosted on https://people.debian.org/~USER/ or https://anonscm.debian.org/cgit/users/USER/.