feat: upgrade to postgresql 15

Dockerfile

@@ -1,7 +1,12 @@
 FROM kopia/kopia:0.15.0
 
 ENV DEBIAN_FRONTEND=noninteractive
-RUN apt-get update && apt-get install -y cron postgresql-client lftp && rm -rf /var/lib/apt/lists/*
+RUN apt-get update && apt-get install -y gnupg2 wget lsb-release
+
+RUN echo "deb http://apt.postgresql.org/pub/repos/apt/ $(lsb_release -cs)-pgdg main" > /etc/apt/sources.list.d/pgdg.list
+RUN wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | apt-key add -
+
+RUN apt-get update && apt-get install -y cron postgresql-client-15 lftp && rm -rf /var/lib/apt/lists/*
 
 ARG KOPIA_CRON_SCHEDULE
 ENV KOPIA_CRON_SCHEDULE ${KOPIA_CRON_SCHEDULE}