[CI]: Update container images

[TomAugspurger]

• moved pctasks-frontend to an aux server
• shrink container images a bit

Trying to fix the CI failures at https://github.com/microsoft/planetary-computer-tasks/actions/runs/5579847626/jobs/10195946932#step:11:419, where we seem to be running out of disk space.

--- ErrImagePull: rpc error: code = Unknown desc = failed to pull and unpack image "localhost:5001/pctasks-ingest:latest": failed to extract layer sha256:d32bc1b36f4802dd6c638c4501c6eb836f140b71383c0d5e87db50115060811a: write /var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/285/fs/opt/az/lib/python3.10/site-packages/azure/synapse/artifacts/models/__pycache__/_models_py3.cpython-310.pyc: no space left on device: unknown

[419](https://github.com/microsoft/planetary-computer-tasks/actions/runs/5579847626/jobs/10195946932#step:11:420)

[TomAugspurger]

3403573 fixes an issue where local dev files like .mypy_cache might have been copied in to the container image. I don't know if this affected the images on CI (probably not) but it made my local image ~200 MB smaller)

e9ef5f8 disables the pip cache, which saves ~20MB.

[TomAugspurger]

The next big target is the task-* images. Currently, pctasks-task-base is >2.5GB.

See the diff below for a way to get it down to ~370MB.

diff --git a/Dockerfile.task_base b/Dockerfile.task_base
index c60bbeb..2cffc3b 100644
--- a/Dockerfile.task_base
+++ b/Dockerfile.task_base
@@ -1,4 +1,4 @@
-FROM ubuntu:20.04
+FROM python:3.9-slim
 
 # Setup timezone info
 ENV TZ=UTC
@@ -9,31 +9,6 @@ ENV PIP_NO_CACHE_DIR=1
 
 RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone
 
-RUN apt-get update && apt-get install -y software-properties-common
-
-RUN add-apt-repository ppa:ubuntugis/ppa && \
-     apt-get update && \
-     apt-get install -y build-essential python3-dev python3-pip \
-     jq unzip ca-certificates wget curl git && \
-     apt-get autoremove && apt-get autoclean && apt-get clean
-
-RUN update-alternatives --install /usr/bin/python python /usr/bin/python3 10
-
-# See https://github.com/mapbox/rasterio/issues/1289
-ENV CURL_CA_BUNDLE=/etc/ssl/certs/ca-certificates.crt
-
-# Install Python 3.8
-RUN curl -L -O "https://github.com/conda-forge/miniforge/releases/latest/download/Mambaforge-$(uname)-$(uname -m).sh" \
-   && bash "Mambaforge-$(uname)-$(uname -m).sh" -b -p /opt/conda \
-   && rm -rf "Mambaforge-$(uname)-$(uname -m).sh"
-
-ENV PATH /opt/conda/bin:$PATH
-ENV LD_LIBRARY_PATH /opt/conda/lib/:$LD_LIBRARY_PATH
-
-RUN mamba install -y -c conda-forge python=3.8 gdal pip setuptools cython numpy
-
-RUN python -m pip install --upgrade pip
-
 # Install common packages
 COPY requirements-task-base.txt /tmp/requirements.txt
 RUN python -m pip install --no-build-isolation -r /tmp/requirements.txt
diff --git a/requirements-task-base.txt b/requirements-task-base.txt
index 3de345b..39fe26a 100644
--- a/requirements-task-base.txt
+++ b/requirements-task-base.txt
@@ -1,2 +1,2 @@
 pystac[validation]==1.*
-rasterio==1.3.0 --no-binary=rasterio
\ No newline at end of file
+rasterio==1.3.0
\ No newline at end of file

This removes a bunch of "cruft" from the task-base Dockerfile. But we need to confirm whether any of that cruft is actually load-bearing.

• Which base image do we need? Do we need ubuntu or can we use some other image?
• Do we need conda / mamba?
• Do we need to build rasterio from source?

[TomAugspurger]

CI passed, so I'll punt on the questions from the previous comment.