build(pipeline): install the destinations tap in the image

meltano install would resolve it from pip_url, but five of the six custom
taps are also installed explicitly and a new plugin failing to appear is
not something you want to debug from a deploy log.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BvdDKvFFSZuMVDH5fEyTob

pipeline/Dockerfile

@@ -18,6 +18,7 @@ COPY plugins/ plugins/
 RUN pip install --no-cache-dir \
     ./plugins/extractors/tap-uk-gias \
     ./plugins/extractors/tap-uk-ees \
+    ./plugins/extractors/tap-uk-ees-destinations \
     ./plugins/extractors/tap-uk-ofsted \
     ./plugins/extractors/tap-uk-fbit \
     ./plugins/extractors/tap-uk-idaci