Bump mkdocs-include-markdown-plugin from 4.0.4 to 5.1.0 in /docs

Bumps [mkdocs-include-markdown-plugin](https://github.com/mondeja/mkdocs-include-markdown-plugin) from 4.0.4 to 5.1.0.
- [Release notes](https://github.com/mondeja/mkdocs-include-markdown-plugin/releases)
- [Commits](mondeja/mkdocs-include-markdown-plugin@v4.0.4...v5.1.0)

---
updated-dependencies:
- dependency-name: mkdocs-include-markdown-plugin
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

docs/requirements.txt

@@ -1,3 +1,3 @@
 mkdocs==1.4.3
-mkdocs-include-markdown-plugin==4.0.4
+mkdocs-include-markdown-plugin==5.1.0
 markdown-callouts==0.3.0