conf.py: rename :cve: role to :cve_nist:

Newer versions of Sphinx already define a :cve: role that points to
cve.org, instead of the role we defined in conf.py that points to
nvd.nist.gov.

Rename our role to :cve_nist: to avoid warnings (treated as errors).
This is also backwards compatible, meaning we can build the doc with an
older Sphinx if needed.

The file were automatically replaced with following command:

find . -name '*.rst' -exec sed -i 's/:cve:/:cve_nist:/g' {} \+

Cherry pick:

* remove changes to release-notes-5.1.rst, does not exist on this branch.

* release-notes-5.0.4.rst: apply the command to this file as it was
  treated previously.

Suggested-By: Quentin Schulz <quentin.schulz@cherry.de>
Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>
(From yocto-docs rev: 5b86879b3b5f3c51bc7fa5dd2848cf1153a22242)

Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
(cherry picked from commit 15fa3b7e85dde50d7236c1738ad607531cc654b8)
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

documentation/contributor-guide/recipe-style-guide.rst

@@ -395,7 +395,7 @@ one CVE is fixed, separate them using spaces.
 CVE Examples
 ------------
 
-This should be the header of patch that fixes :cve:`2015-8370` in GRUB2::
+This should be the header of patch that fixes :cve_nist:`2015-8370` in GRUB2::
 
    grub2: Fix CVE-2015-8370