Re-enable strict mode in docs vlidation. Bump mkdocs-material version (#3073)

- Re-enable strict mode in the verify docs command now that the latest version of mkdocs-material is available and supports the new Google Analytics layout
- Amend mkdocs config to use the new Google Analytics layout
- Bump to use latest 1.2 version of mkdocs

Note - current issue https://github.com/mkdocs/mkdocs/issues/2457 stops live reload from work in mkdocs 1.2 so developers will need to amend the mkdocs.yml
to pin mkdocs to version 1.1.2

Signed-off-by: Steve Richards <srichards@mirantis.com>

mkdocs/requirements.txt

@@ -1,8 +1,8 @@
 # Direct dependencies
-mkdocs>=1.1
+mkdocs>=1.2
 Pygments>=2.4
 markdown>=3.2
 pymdown-extensions>=7.0
 mkdocs-material-extensions>=1.0
 mkdocs-git-revision-date-localized-plugin>=0.7.3
-mkdocs-material>=6.1.0
+mkdocs-material>=7.1.8