TechDocs: Add changesets for deprecation and proper caching

.changeset/techdocs-green-singers-jump.md

@@ -0,0 +1,6 @@
+---
+'@backstage/techdocs-common': minor
+'@backstage/plugin-techdocs-backend': minor
+---
+
+URL Preparer will now use proper etag based caching introduced in https://github.com/backstage/backstage/pull/4120. Previously, builds used to be cached for 30 minutes.

.changeset/techdocs-new-needles-arrive.md

@@ -0,0 +1,8 @@
+---
+'@backstage/techdocs-common': patch
+'@backstage/plugin-techdocs-backend': patch
+---
+
+TechDocs will throw warning in backend logs when legacy git preparer or dir preparer is used to preparer docs. Migrate to URL Preparer by updating `backstage.io/techdocs-ref` annotation to be prefixed with `url:`.
+Detailed docs are here https://backstage.io/docs/features/techdocs/how-to-guides#how-to-use-url-reader-in-techdocs-prepare-step
+See benefits and reason for doing so https://github.com/backstage/backstage/issues/4409

plugins/techdocs-backend/src/service/router.ts

@@ -184,7 +184,7 @@ export async function createRouter({
             );
             // TODO: re-trigger build for cache invalidation.
             // Add build info in techdocs_metadata.json and compare it against
-            // the eTag/commit in the repository.
+            // the etag/commit in the repository.
             // Without this, docs will not be re-built once they have been generated.
             // Although it is unconventional that anyone will face this issue - because
             // if you have an external storage, you should be using CI/CD to build and publish docs.