DeepL connector: retry policy, 17.4.0 and 18.2.0

DeepL connector: retries DeepL rate limits and dropped connections with exponential backoff, using the resilience pipeline that now ships in Translation Manager 17.9.0 / 18.3.0. Bad API key, exhausted quota and unknown glossary still fail straight away
DeepL connector: removed the Throttle setting (forced to 0). Added a Retries box to the config page (toggle, count, base delay), with retry on by default
DeepL connector: moved off the Translation Manager nightly packages onto the released 17.9.0 ones and dropped the temporary NuGet.Config
DeepL connector: forward-merged v17 into v18 with a merge commit, so the branch history stays intact for the next forward-port
Released 17.4.0 and 18.2.0 to NuGet