Set mirror and stats in p2 site's artifacts

[LorenzoBettini]

See xtext/xtext-monorepo#13

maybe for the next milestone M1

[LorenzoBettini]

Mirror has been configured in 2e9ada1

[cdietrich]

@LorenzoBettini what is left for this issue?

[LorenzoBettini]

@cdietrich the download stats haven't been implemented. I don't know whether those stats still have to be configured explicitly: I can already access Xtext download statistics anyway. The mirror part is complete. I think we can close this as complete.

[LorenzoBettini]

Just an additional note: mirroring for 2.31 works as expected: while Oomphing one of my Xtext installations I see

Mirrored 46 artifacts from https://eclipse.mirror.garr.it/modeling/tmf/xtext/updates/releases/2.31.0/ at 2,508kb/s
Mirrored 44 artifacts from https://mirror.dogado.de/eclipse/modeling/tmf/xtext/updates/releases/2.31.0/ at 1,832kb/s
Mirrored 20 artifacts from https://ftp.fau.de/eclipse/modeling/tmf/xtext/updates/releases/2.31.0/ at 1,319kb/s

:)