deploy: update SQLite build script

Allow overriding the base image and the target os/arch.

deploy/install-sqlite3.sh

@@ -2,6 +2,11 @@
 #
 # Build the SQLite3 CLI from source for linux/amd64.
 #
+# Optional parameters:
+#
+#   BUILDBASE: base image (e.g., ubuntu:22.04)
+#   PLATFORM:  os/arch    (e.g., linux/amd64)
+#
 set -euo pipefail
 
 here="$(dirname ${BASH_SOURCE[0]})"
@@ -19,12 +24,13 @@ year="$(echo "$latest" | cut -d/ -f1)"
 vers="$(echo "$latest" | cut -d- -f3 | cut -d. -f1)"
 
 img=sqlite3-builder:latest
-plat=linux/amd64
+buildbase="${BUILDBASE:-ubuntu:22.04}"
+plat="${PLATFORM:-linux/amd64}"
 out=./sqlite3-"$vers"
 dl="$base/$latest"
 
 cat <<EOF | docker build -t "$img" -
-FROM --platform="$plat" ubuntu:22.04 as builder
+FROM --platform="$plat" ubuntu:20.04 as builder
 
 WORKDIR /root