Upload custom extensions to S3 (#4585)

## Problem

We want to have a number of custom extensions that will not be available
by default, as an example of such is [Postgres
Anonymizer](https://postgresql-anonymizer.readthedocs.io/en/stable/)
(please note that the extension should be added to
`shared_preload_libraries`). To distinguish them, custom extensions
should be added to a different S3 path:

```
s3://<bucket>/<release version>/<postgres_version>/<ext_name>/share/extensions/
s3://<bucket>/<release version>/<postgres_version>/<ext_name>/lib

where <ext_name> is an extension name
```

Resolves https://github.com/neondatabase/neon/issues/4582

## Summary of changes
- Add Postgres Anonymizer extension to Dockerfile (it's included only to
postgres-extensions target)
- Build extensions image from postgres-extensions target in a workflow
- Upload custom extensions to S3 (different directory)

Dockerfile.compute-node

@@ -515,6 +515,26 @@ RUN wget https://github.com/ChenHuajun/pg_roaringbitmap/archive/refs/tags/v0.5.4
     make -j $(getconf _NPROCESSORS_ONLN) install && \
     echo 'trusted = true' >> /usr/local/pgsql/share/extension/roaringbitmap.control
 
+#########################################################################################
+#
+# Layer "pg-anon-pg-build"
+# compile anon extension
+#
+#########################################################################################
+FROM build-deps AS pg-anon-pg-build
+COPY --from=pg-build /usr/local/pgsql/ /usr/local/pgsql/
+
+# Kaniko doesn't allow to do `${from#/usr/local/pgsql/}`, so we use `${from:17}` instead
+ENV PATH "/usr/local/pgsql/bin/:$PATH"
+RUN wget https://gitlab.com/dalibo/postgresql_anonymizer/-/archive/1.1.0/postgresql_anonymizer-1.1.0.tar.gz -O pg_anon.tar.gz && \
+    echo "08b09d2ff9b962f96c60db7e6f8e79cf7253eb8772516998fc35ece08633d3ad pg_anon.tar.gz" | sha256sum --check && \
+    mkdir pg_anon-src && cd pg_anon-src && tar xvzf ../pg_anon.tar.gz --strip-components=1 -C . && \
+    find /usr/local/pgsql -type f | sort  > /before.txt && \
+    make -j $(getconf _NPROCESSORS_ONLN) install PG_CONFIG=/usr/local/pgsql/bin/pg_config && \
+    echo 'trusted = true' >> /usr/local/pgsql/share/extension/anon.control && \
+    find /usr/local/pgsql -type f | sort  > /after.txt && \
+    /bin/bash -c 'for from in $(comm -13 /before.txt /after.txt); do to=/extensions/anon/${from:17} && mkdir -p $(dirname ${to}) && cp -a ${from} ${to}; done'
+
 #########################################################################################
 #
 # Layer "rust extensions"
@@ -623,6 +643,7 @@ RUN wget https://github.com/pksunkara/pgx_ulid/archive/refs/tags/v0.1.0.tar.gz -
 #
 #########################################################################################
 FROM build-deps AS neon-pg-ext-build
+# Public extensions
 COPY --from=postgis-build /usr/local/pgsql/ /usr/local/pgsql/
 COPY --from=postgis-build /sfcgal/* /
 COPY --from=plv8-build /usr/local/pgsql/ /usr/local/pgsql/
@@ -704,8 +725,15 @@ RUN rm /usr/local/pgsql/lib/lib*.a
 #
 #########################################################################################
 FROM scratch AS postgres-extensions
-COPY --from=postgres-cleanup-layer /usr/local/pgsql/share/extension /usr/local/pgsql/share/extension
-COPY --from=postgres-cleanup-layer /usr/local/pgsql/lib             /usr/local/pgsql/lib
+# After the transition this layer will include all extensitons.
+# As for now, it's only for new custom ones
+#
+# # Default extensions
+# COPY --from=postgres-cleanup-layer /usr/local/pgsql/share/extension /usr/local/pgsql/share/extension
+# COPY --from=postgres-cleanup-layer /usr/local/pgsql/lib             /usr/local/pgsql/lib
+# Custom extensions
+COPY --from=pg-anon-pg-build /extensions/anon/lib/ /extensions/anon/lib
+COPY --from=pg-anon-pg-build /extensions/anon/share/extension /extensions/anon/share/extension
 
 #########################################################################################
 #