Fix: make index and llmindex init wait for tesseract language install (#14670)

* Fix: make index and llmindex init wait for tesseract language install

* Updates this out of date diagram and makes it Mermaid

docker/init-flow.md

@@ -0,0 +1,57 @@
+# Container init flow
+
+Startup order of the s6-rc oneshot services under `docker/rootfs/etc/s6-overlay/s6-rc.d/`. An arrow `A --> B` means B lists A in its `dependencies.d/`, so B waits for A. Redundant (transitive) edges are omitted.
+
+Each labelled box is a group of services that can run in parallel: every service in it starts as soon as its own dependencies finish, so services in the same box run in parallel. A service does not wait for the rest of its group, only for the arrows pointing at it. Long-running services such as `init-tesseract-langs` (package installs) overlap with several later steps.
+
+```mermaid
+flowchart TD
+    subgraph w3 ["Run in parallel"]
+        init-tesseract-langs
+        init-modify-user
+        init-wait-for-db
+        init-wait-for-redis
+    end
+    subgraph w4 ["Run in parallel"]
+        init-folders
+        init-compile-bytecode
+    end
+    subgraph w6 ["Run in parallel"]
+        init-search-index
+        init-llmindex-migrate
+        init-superuser
+    end
+
+    base --> init-start --> init-env-file
+
+    init-env-file --> init-tesseract-langs
+    init-env-file --> init-modify-user
+    init-env-file --> init-wait-for-db
+    init-env-file --> init-wait-for-redis
+    init-start --> init-compile-bytecode
+
+    init-modify-user --> init-folders
+    init-modify-user --> init-compile-bytecode
+
+    init-folders --> init-migrations
+    init-compile-bytecode --> init-migrations
+    init-wait-for-db --> init-migrations
+
+    init-migrations --> init-search-index
+    init-migrations --> init-llmindex-migrate
+    init-migrations --> init-superuser
+
+    init-tesseract-langs --> init-search-index
+    init-tesseract-langs --> init-llmindex-migrate
+    init-tesseract-langs --> init-system-checks
+    init-superuser --> init-system-checks
+
+    init-search-index --> init-custom-init
+    init-system-checks --> init-custom-init
+    init-wait-for-redis --> init-custom-init
+
+    init-custom-init --> init-complete
+    init-llmindex-migrate --> init-complete
+```
+
+`init-search-index` and `init-llmindex-migrate` run `manage.py`, which runs the Django system checks, including the check that the configured OCR languages are installed, so they wait for `init-tesseract-langs`.