Add collection migration example and guide

examples/go-library/prepare/collections/support/fragments/resources.yaml

@@ -0,0 +1,28 @@
+backends:
+  offline:
+    endpoint: https://example.invalid/v1
+profiles:
+  base:
+    backend: support/offline
+    model: offline-model
+    timeout_seconds: 90
+  fast:
+    extends: base
+    timeout_seconds: 60
+prompts:
+  prepare:
+    version: "1.0.0"
+    default_profile: support/fast
+    description: Prepare a prompt without contacting a model provider.
+    inputs:
+      - name: note
+        required: true
+        content_type: text/plain
+    messages:
+      - role: system
+        content: Summarize the note in one sentence.
+      - role: user
+        content_file: ../messages/note.md
+    output:
+      format: text
+      validation_mode: basic