Publish metadata updates over ActivityPub

[pombredanne]

To advertise the availability of new package or vulnerabilities metadata, we need to build an application in PurlDB or in VulnerableCode (VCIO) that creates a user for each "package" on an ActivityPub (AP) server and can posts to the server to advertise the data updates from new scans or new versions. We may need to define extensions to ActivityPub as needed.
The outcome could be:

• Create an app to manage the many "package" ActivityPub accounts
• Advertise the metadata updates over ActivityPub on new metadata

[keshav-space]

Completed in: #44

The simple way to test this is to follow the below steps after installing FederatedCode (https://github.com/aboutcode-org/federatedcode?tab=readme-ov-file#quick-installation):

1. Create superuser python manage.py createsuperuser
2. Login to federatedcode admin panel http://127.0.0.1:8000/admin/
3. Go to http://127.0.0.1:8000/admin/fedcode/service/add/ and create service slect newly created superuser as user, and leave remote-actor empty.
4. Go to go to http://127.0.0.1:8000/create-repo and add https://github.com/aboutcode-org/aboutcode-packages-npm-385
5. Run python3 manage.py sync sync_scancode_scans to sync scan
6. Install federatedcode client using pip install aboutcode.federatedcode
7. Go to http://127.0.0.1:8000/purls/@pkg:npm/atlasboard/ to get the scan advertisement for pkg:npm/atlasboard

[pombredanne]

The app to create AP account is based in the the pipelines here https://github.com/aboutcode-org/federatedcode/tree/main/fedcode/pipelines that handle the package ActivityPub creation/update/deletion using the "sync" command