docs(tools/build-docs): render plugin DOCUMENTATION blocks into the MkDocs site

The Linuxfabrik LFOps documentation site only covered roles and the top-
level project pages. Modules, lookup plugins and filter plugins had to be
discovered via `ansible-doc` on a checkout. This commit extends
`tools/build-docs` so every Python file under `plugins/{modules,lookup,
filter}/` that carries an Ansible-style `DOCUMENTATION` block is rendered
into Markdown and added to the site navigation.

Implementation

* AST-based extraction of the DOCUMENTATION (parsed YAML), EXAMPLES (raw
  string), and RETURN (parsed YAML) module-level constants.
* Markdown renderer that emits a header, synopsis, optional version-added,
  requirements list, parameters table (with suboptions folded into the
  description column), examples code block, return values table, notes,
  and authors.
* Per-kind output directory: `docs/modules/`, `docs/lookup/`, `docs/filter/`,
  with stale `.md` files cleaned up before each rebuild.
* Name-collision handling: pages keep their bare name in the nav unless a
  plugin name is shared across more than one kind (e.g. `bitwarden_item`
  exists both as a module and as a lookup plugin); collisions get a
  ` (lookup)` / ` (filter)` suffix in the nav label.

Navigation

The nav is reorganised so the project meta pages (Home, Compatibility,
Playbooks, STIGs, Security, Contributing) live under a single
"Linuxfabrik LFOps" section, with "Roles" and "Modules" as the two
technical sibling sections below. The site Home page is now a symlink to
the repository's `README.md` (badges, hero block, the full table of
contents, all included), so the docs site landing page matches the
GitHub README without manual sync.

Drive-by

`plugins/modules/uptimerobot_monitor.py` carried two description bullets
of the form "For C(type=keyw): C(exist) alerts ...". The colon ended the
YAML key prematurely, so its DOCUMENTATION did not parse. Reworded to
"For C(type=keyw), C(exist) alerts ..." (and the analogous spot for
sub_type), and the page renders.

`.gitignore` gains the four new auto-generated paths (`/docs/index.md`,
`/docs/modules/`, `/docs/lookup/`, `/docs/filter/`); the previously
hand-curated `docs/index.md` is removed from tracking.

Author: markuslf

.gitignore

@@ -14,6 +14,10 @@ particle/.vagrant
 /docs/CODE_OF_CONDUCT.md
 /docs/compatibility.md
 /docs/contributing.md
+/docs/filter/
+/docs/index.md
+/docs/lookup/
+/docs/modules/
 /docs/playbooks.md
 /docs/roles/
 /docs/security.md

docs/index.md

@@ -71,8 +71,8 @@
         required: false
     sub_type:
         description:
-            - For C(type=port): which protocol/port preset to use. C(custom)
-              means "use the explicit C(port) value".
+            - For C(type=port), which protocol/port preset to use. C(custom)
+              means 'use the explicit C(port) value'.
         type: str
         choices: ['custom', 'ftp', 'http', 'https', 'imap', 'pop3', 'smtp']
         required: false
@@ -83,7 +83,7 @@
         required: false
     keyword_type:
         description:
-            - For C(type=keyw): C(exist) alerts when the keyword is found,
+            - For C(type=keyw), C(exist) alerts when the keyword is found,
               C(notex) alerts when it is missing.
         type: str
         choices: ['exist', 'notex']