These are by the far the longest time spent on during a migration.
Indicate the progress of how many issues and PRs were migrated so far.
Don't overwhelm the messenger, so they are only updated once a batch is
migrated. Which is "slow" enough to see it's not stuck and still doing work.
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/12738
Reviewed-by: Ellen Εμίλια Άννα Zscheile <fogti@noreply.codeberg.org>
Reviewed-by: 0ko <0ko@noreply.codeberg.org>
