plantuml: Generate images manually so we are serving static data

Unfortunately, all the VitePress PlantUML plugins either display the data by
sending to a remote server (plantuml.com), or require Java and the PlantUML
JAR to be installed locally.

To keep installation and development of the documentation straightforward, for
now require that PlantUML graphics be generated manually.  This shouldn't be
needed to be done often - and the process to generate is easy if Docker
is available.

Author: slusarz

assets/plantuml/README.md

@@ -0,0 +1,30 @@
+# PlantUML Data
+
+This directory contains PlantUML files that are used to create diagrams for
+the documentation.
+
+## Docker
+
+[PlantUML](https://plantuml.com/) files are converted to SVG by using a Java
+program.
+
+It is easiest to run the program by using a pre-configured Docker container.
+
+The output command is as follows:
+
+```
+docker run --rm -v /path/to/your/puml/files:/data \
+  -v /path/to/your/output/directory:/output plantuml/plantuml \
+  -tsvg /data/your_diagram.puml \
+  -o /output
+```
+
+For example, if running from this directory to convert foo.puml, and storing
+the SVG file in the "docs/core/images" directory (so it can be referenced via
+Markdown from within VitePress), run:
+
+```
+mkdir -p ../../docs/core/images
+docker run --rm -v ./:/data -v ../../docs/core/images:/output \
+  plantuml/plantuml -tsvg /data/foo.puml -o /output
+```

docs/core/config/include/submission_flow.inc renamed to assets/plantuml/submission_flow.puml

@@ -84,7 +84,7 @@ service:
 
 ## Flow Diagram
 
-<!-- @include: @docs/core/config/include/submission_flow.inc -->
+![Submission Flow Diagram](/docs/core/config/images/submission_flow.svg)
 
 ## Configuration
 

docs/core/config/images/submission_flow.svg

@@ -1,7 +1,6 @@
 import containerPlugin from 'markdown-it-container'
 import fg from 'fast-glob'
 import deflistPlugin from 'markdown-it-deflist'
-import { plantuml } from "@mdit/plugin-plantuml";
 import path from 'path'
 import { createMarkdownRenderer } from 'vitepress'
 import { dovecotSetting, frontmatterIter, loadData } from './utility.js'
@@ -18,7 +17,6 @@ export function dovecotMdExtend(md) {
 	})
 	md.use(deflistPlugin)
 	md.use(dovecot_markdown)
-	md.use(plantuml)
 
 	return md
 }

docs/core/config/submission.md

@@ -1,7 +1,6 @@
 {
   "name": "dovecot-ce-documentation",
   "devDependencies": {
-    "@mdit/plugin-plantuml": "^0.22.3",
     "@sindresorhus/slugify": "^2.2.1",
     "camelcase": "^8.0.0",
     "commander": "^13.1.0",