Use link name in activities

[rullzer]

Now that we can have multiple link shares it would be good to use that in the activities to have some more traceability.

Assume:

1. userA creates a public link for externalB and a public link for externalC and names them the same
2. externalB opens the link and uploads a new file 'X'
3. externalC opens the link and also uplaods a new file 'Y'

Then in your activity stream you would see:

• externalB (via link share) added file X
• externalC (via link share) added file Y

CC: @nickvergessen @MorrisJobke

[wiswedel]

Even though this would be nice indeed, it requires the finalization of the of oc_share.label implementation on the web UI first, in order to identify the several shares properly.

[wiswedel]

depends on https://github.com/nextcloud/server/issues/15500

[tcitworld]

Since #21357 is merged this should now be possible.