Create activity preview UI components for unimplemented object types (eg Video, Event,...)

[mayel]

We support including them in feeds using the APActivity json object (https://github.com/bonfire-networks/bonfire-app/issues/44), but need nice ways to view them

• [x] pictures (eg pixelfed)
• [x] video (eg. peertube)
• [x] events (eg. mobilizon, https://gancio.org -> need a sample JSON from the latter)
• [x] audio / podcasts (eg. castopod)
• [x] longform posts (eg. writefreely/writeas)
• [x] books (eg bookwormhole)
• [x] live streaming media (eg. Owncast and https://codeberg.org/namekuji/audon/wiki/Home)

[mayel]

Added ActivityPub.Fixtures.insert_all as a way to populate the dev DB with a bunch of example AP data

[loid345]

Don't forget about discourse https://meta.discourse.org/t/activitypub-plugin/266794/67