Link to migration bundles

Any task bundles that have migrations are linked by the newer task
bundles by a dedicated annotation. See the following example task
bundles:

  tb0 -->  tb1 --> tb2 --> tb3 --> tb4 --> tb5
           |               |
           M               M

where, tb2 and tb3 point to tb1, and tb4 and tb5 point to tb3.

Linking task bundles helps to reduce the number of HTTP requests made to
Quay.io that query which task bundles have migrations.

Terms:

- tb means task bundle.
- M means migration.

hack/build-and-push.sh

@@ -228,6 +228,7 @@ build_push_task() {
     local -r task_bundle=$3
     local -r task_file_sha=$4
     local -r has_migration=$5
+    local -r prev_bundle_digest=$6
 
     local -r task_description=$(yq e '.spec.description' "$prepared_task_file" | head -n 1)
 
@@ -253,6 +254,8 @@ build_push_task() {
         ANNOTATIONS+=("dev.konflux-ci.task.migration=true")
     fi
 
+    ANNOTATIONS+=("dev.konflux-ci.task/previous-migration-bundle=${prev_bundle_digest}")
+
     local -a ANNOTATION_FLAGS=()
     for annotation in "${ANNOTATIONS[@]}"; do
         ANNOTATION_FLAGS+=("--annotate" "$(escape_tkn_bundle_arg "$annotation")")
@@ -431,6 +434,34 @@ attach_migration_file() {
     return 0
 }
 
+# Find previous bundle that has a migration and output its digest.
+find_previous_migration_bundle_digest() {
+    local -r task_name=${1:?Missing task name}
+    local -r task_version=${2:?Missing task version}
+    local -r repo=${TEST_REPO_NAME:-task-${task_name}}
+
+    local -r url_list_recent_tags="https://quay.io/api/v1/repository/${QUAY_NAMESPACE}/${repo}/tag/?onlyActiveTags=true"
+    local -r expr_filter_tags=".tags[] | select(.name | test(\"^(${task_name}-)?${task_version}-[0-9a-f]+\$\")) | .manifest_digest"
+
+    local prev_bundle_digest has_migration
+
+    curl --fail -sL "$url_list_recent_tags" | jq -r "$expr_filter_tags" | \
+        while read -r manifest_digest; do
+            curl --fail -sL -o /tmp/manifest.json \
+                "https://quay.io/v2/${QUAY_NAMESPACE}/${repo}/manifests/${manifest_digest}"
+            prev_bundle_digest=$(jq -r '.annotations."dev.konflux-ci.task/previous-migration-bundle"' </tmp/manifest.json)
+            has_migration=$(jq -r '.annotations."dev.konflux-ci.task.migration"' </tmp/manifest.json)
+            if [ "$has_migration" == "true" ]; then
+                echo "$manifest_digest"
+                return
+            fi
+            if [ "$prev_bundle_digest" == "null" ] || [ -z "$prev_bundle_digest" ]; then
+                echo
+                return
+            fi
+        done
+}
+
 build_push_tasks() {
     local build_data
     local task_bundle_with_digest
@@ -440,6 +471,7 @@ build_push_tasks() {
     local task_bundle
     local output
     local has_migration
+    local prev_bundle_digest
 
     find task/*/* -maxdepth 0 -type d | awk -F '/' '{ print $0, $2, $3 }' | \
     while read -r task_dir task_name task_version
@@ -479,9 +511,15 @@ build_push_tasks() {
             task_bundle_with_digest=${task_bundle}@${digest}
             echo "info: use existing $task_bundle_with_digest" 1>&2
         else
+            echo "info: finding the previous task bundle that has a migration" 1>&2
+            prev_bundle_digest=$(find_previous_migration_bundle_digest "$task_name" "$task_version")
+
             echo "info: push new bundle $task_bundle" 1>&2
 
-            output=$(build_push_task "$task_dir" "$prepared_task_file" "$task_bundle" "$task_file_sha" "$has_migration")
+            output=$(
+                build_push_task "$task_dir" "$prepared_task_file" "$task_bundle" "$task_file_sha" \
+                    "$has_migration" "$prev_bundle_digest"
+            )
 
             task_bundle_with_digest=$(grep -m 1 "^Pushed Tekton Bundle to" <<<"$output" 2>/dev/null)
             task_bundle_with_digest=${task_bundle_with_digest##* }
@@ -501,7 +539,6 @@ build_push_tasks() {
 
 build_push_tasks
 
-
 # Used for build-definitions pull request CI only
 if [ -n "$ENABLE_SOURCE_BUILD" ]; then
     for pipeline_yaml in "$GENERATED_PIPELINES_DIR"/*.yaml; do