uSync: Umbraco 17.8 readiness

Repo: KevinJump/uSync

uSync: RTE dependencies now pick up URL-encoded %7BlocalLink:…%7D links, which 17.8 resolves
uSync: logs the server role at startup. 17.8 elects the role before the startup import, so on load-balanced sites using election only the SchedulingPublisher runs it (checked with two sites sharing a SQLite DB)
uSync: dashboard SignalR hub auto-reconnects with a capped backoff and a fresh token per reconnect
uSync: a content key change now also clears the old key's URL alias rows
Ran the test suite against the 17.8.0-rc packages, and on 17.8.0-rc checked the #1097 block variance scenario and a backoffice-only site without AddWebsite()
Merged all four into v17/17.5.0; release PR to v17/main is open