doc: fix 404 page

Sphinx handling of 404 page is not that easy when using theme
customizations. Enabled the `sphinx-notfound-page` extension (maintained
by readthedocs) to fix its displaying.

Also adjusted Zephyr logo (was causing some Sphinx processing errors
when trying to scale it).

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>

doc/404.rst

@@ -7,7 +7,6 @@ Sorry, Page Not Found
 
 .. image:: images/Zephyr-Kite-in-tree.png
    :align: right
-   :scale: 25%
 
 .. raw:: html
 

doc/conf.py

@@ -82,6 +82,7 @@ extensions = [
     "sphinx_tabs.tabs",
     "zephyr.warnings_filter",
     "zephyr.doxyrunner",
+    "notfound.extension",
 ]
 
 # Only use SVG converter when it is really needed, e.g. LaTeX.
@@ -203,6 +204,10 @@ html_redirect_pages = redirects.REDIRECTS
 warnings_filter_config = str(ZEPHYR_BASE / "doc" / "known-warnings.txt")
 warnings_filter_silent = False
 
+# -- Options for notfound.extension ---------------------------------------
+
+notfound_urls_prefix = f"/{version}/"
+
 # -- Linkcheck options ----------------------------------------------------
 
 extlinks = {

scripts/requirements-doc.txt

@@ -6,6 +6,7 @@ sphinx_rtd_theme>=0.5.2,<1.0
 sphinx-tabs
 sphinxcontrib-svg2pdfconverter
 pygments~=2.9
+sphinx-notfound-page>=0.6
 
 # Used by zephyr_module
 pykwalify