fast imports: initial Importer and Storage changes (#9218)

Co-authored-by: Heikki Linnakangas <heikki@neon.tech>
Co-authored-by: Stas Kelvic <stas@neon.tech>

# Context

This PR contains PoC-level changes for a product feature that allows
onboarding large databases into Neon without going through the regular
data path.

# Changes

This internal RFC provides all the context
* https://github.com/neondatabase/cloud/pull/19799

In the language of the RFC, this PR covers

* the Importer code (`fast_import`) 
* all the Pageserver changes (mgmt API changes, flow implementation,
etc)
* a basic test for the Pageserver changes

# Reviewing

As acknowledged in the RFC, the code added in this PR is not ready for
general availability.
Also, the **architecture is not to be discussed in this PR**, but in the
RFC and associated Slack channel instead.

Reviewers of this PR should take that into consideration.
The quality bar to apply during review depends on what area of the code
is being reviewed:

* Importer code (`fast_import`): practically anything goes
* Core flow (`flow.rs`):
* Malicious input data must be expected and the existing threat models
apply.
* The code must not be safe to execute on *dedicated* Pageserver
instances:
* This means in particular that tenants *on other* Pageserver instances
must not be affected negatively wrt data confidentiality, integrity or
availability.
* Other code: the usual quality bar
* Pay special attention to correct use of gate guards, timeline
cancellation in all places during shutdown & migration, etc.
* Consider the broader system impact; if you find potentially
problematic interactions with Storage features that were not covered in
the RFC, bring that up during the review.

I recommend submitting three separate reviews, for the three high-level
areas with different quality bars.


# References

(Internal-only)

* refs https://github.com/neondatabase/cloud/issues/17507
* refs https://github.com/neondatabase/company_projects/issues/293
* refs https://github.com/neondatabase/company_projects/issues/309
* refs https://github.com/neondatabase/cloud/issues/20646

---------

Co-authored-by: Stas Kelvich <stas.kelvich@gmail.com>
Co-authored-by: Heikki Linnakangas <heikki@neon.tech>
Co-authored-by: John Spray <john@neon.tech>

compute/compute-node.Dockerfile

@@ -1243,7 +1243,7 @@ RUN make -j $(getconf _NPROCESSORS_ONLN) \
 
 #########################################################################################
 #
-# Compile and run the Neon-specific `compute_ctl` binary
+# Compile and run the Neon-specific `compute_ctl` and `fast_import` binaries
 #
 #########################################################################################
 FROM $REPOSITORY/$IMAGE:$TAG AS compute-tools
@@ -1264,6 +1264,7 @@ RUN cd compute_tools && mold -run cargo build --locked --profile release-line-de
 FROM debian:$DEBIAN_FLAVOR AS compute-tools-image
 
 COPY --from=compute-tools /home/nonroot/target/release-line-debug-size-lto/compute_ctl /usr/local/bin/compute_ctl
+COPY --from=compute-tools /home/nonroot/target/release-line-debug-size-lto/fast_import /usr/local/bin/fast_import
 
 #########################################################################################
 #
@@ -1458,6 +1459,7 @@ RUN mkdir /var/db && useradd -m -d /var/db/postgres postgres && \
 
 COPY --from=postgres-cleanup-layer --chown=postgres /usr/local/pgsql /usr/local
 COPY --from=compute-tools --chown=postgres /home/nonroot/target/release-line-debug-size-lto/compute_ctl /usr/local/bin/compute_ctl
+COPY --from=compute-tools --chown=postgres /home/nonroot/target/release-line-debug-size-lto/fast_import /usr/local/bin/fast_import
 
 # pgbouncer and its config
 COPY --from=pgbouncer         /usr/local/pgbouncer/bin/pgbouncer /usr/local/bin/pgbouncer
@@ -1533,6 +1535,25 @@ RUN apt update && \
     rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/* && \
     localedef -i en_US -c -f UTF-8 -A /usr/share/locale/locale.alias en_US.UTF-8
 
+# s5cmd 2.2.2 from https://github.com/peak/s5cmd/releases/tag/v2.2.2
+# used by fast_import
+ARG TARGETARCH
+ADD https://github.com/peak/s5cmd/releases/download/v2.2.2/s5cmd_2.2.2_linux_$TARGETARCH.deb /tmp/s5cmd.deb
+RUN set -ex; \
+    \
+    # Determine the expected checksum based on TARGETARCH
+    if [ "${TARGETARCH}" = "amd64" ]; then \
+        CHECKSUM="392c385320cd5ffa435759a95af77c215553d967e4b1c0fffe52e4f14c29cf85"; \
+    elif [ "${TARGETARCH}" = "arm64" ]; then \
+        CHECKSUM="939bee3cf4b5604ddb00e67f8c157b91d7c7a5b553d1fbb6890fad32894b7b46"; \
+    else \
+        echo "Unsupported architecture: ${TARGETARCH}"; exit 1; \
+    fi; \
+    \
+    # Compute and validate the checksum
+    echo "${CHECKSUM}  /tmp/s5cmd.deb" | sha256sum -c -
+RUN dpkg -i /tmp/s5cmd.deb && rm /tmp/s5cmd.deb
+
 ENV LANG=en_US.utf8
 USER postgres
 ENTRYPOINT ["/usr/local/bin/compute_ctl"]