Add Oracle Linux image variants

The primary benefits of this are arm64 support (in 8.0) and smaller images (in 5.7 and 8.0).

```console
$ docker images mysql
REPO   TAG         IMAGE-ID      SIZE

mysql  5.6-debian  9e4a20b3bbbc  302MB
mysql  5.6-oracle  929e36226e5f  347MB

mysql  5.7-debian  a4fdfd462add  448MB
mysql  5.7-oracle  526647feecfa  338MB

mysql  8.0-debian  30f937e841c8  541MB
mysql  8.0-oracle  71ceccbba717  381MB
```

Author: tianon

5.6/Dockerfile.oracle

@@ -31,15 +31,18 @@ generated_warning() {
 for version; do
 	export version
 
-	debianVersion="$(jq -r '.[env.version].debian // ""' versions.json)"
-	if [ -n "$debianVersion" ]; then
-		dockerfile='Dockerfile.debian'
-
-		{
-			generated_warning
-			gawk -f "$jqt" "template/$dockerfile"
-		} > "$version/$dockerfile"
-	fi
+	for variant in oracle debian; do
+		export variant
+
+		variantVersion="$(jq -r '.[env.version][env.variant] // {} | .version // ""' versions.json)"
+		if [ -n "$variantVersion" ]; then
+			dockerfile="Dockerfile.$variant"
+			{
+				generated_warning
+				gawk -f "$jqt" "template/$dockerfile"
+			} > "$version/$dockerfile"
+		fi
+	done
 
 	cp -a template/docker-entrypoint.sh "$version/docker-entrypoint.sh"
 done

5.7/Dockerfile.oracle

@@ -6,6 +6,13 @@ declare -A aliases=(
 	[8.0]='8 latest'
 )
 
+defaultDefaultVariant='oracle'
+declare -A defaultVariants=(
+	[5.6]='debian'
+	[5.7]='debian'
+	[8.0]='debian'
+)
+
 self="$(basename "$BASH_SOURCE")"
 cd "$(dirname "$(readlink -f "$BASH_SOURCE")")"
 
@@ -58,9 +65,8 @@ join() {
 
 for version; do
 	export version
-	df='Dockerfile.debian'
-	commit="$(dirCommit "$version" "$df")"
 
+	defaultVariant="${defaultVariants[$version]:-$defaultDefaultVariant}"
 	fullVersion="$(jq -r '.[env.version].version' versions.json)"
 
 	versionAliases=()
@@ -73,11 +79,27 @@ for version; do
 		${aliases[$version]:-}
 	)
 
-	echo
-	cat <<-EOE
-		Tags: $(join ', ' "${versionAliases[@]}")
-		GitCommit: $commit
-		Directory: $version
-		File: $df
-	EOE
+	for variant in oracle debian; do
+		df="Dockerfile.$variant"
+		commit="$(dirCommit "$version" "$df")"
+
+		variantAliases=( "${versionAliases[@]/%/-$variant}" )
+		variantAliases=( "${variantAliases[@]//latest-/}" )
+		if [ "$variant" = "$defaultVariant" ]; then
+			variantAliases=( "${versionAliases[@]}" "${variantAliases[@]}" )
+		fi
+
+		# TODO if the list of architectures supported by MySQL ever is greater than that of the base image it's FROM, this list will need to be filtered
+		export variant
+		variantArches="$(jq -r '.[env.version][env.variant].architectures | join(", ")' versions.json)"
+
+		echo
+		cat <<-EOE
+			Tags: $(join ', ' "${variantAliases[@]}")
+			Architectures: $variantArches
+			GitCommit: $commit
+			Directory: $version
+			File: $df
+		EOE
+	done
 done