Update cms version

Implement task https://gitlab.office.nic.cz/cz.nic/techdep/techdep/-/issues/276.

Update cms version to current 3.11.3.

Subissues:

• #104 (closed) - Fix lint, mypy, tests; Enable explicit python version.
• #105 (closed) - End support for python version < 3.9.
• #106 (closed) - Upgrade versions to the latest Django and DjangoCMS.
• #107 (closed) - Fix status code of error pages when they are cached.
• #108 (closed) - Add support of .well-known/security.txt.
• #109 (closed) - Fix link to youtu.be.
• #111 (closed) - Update version CMS

For old version:

• #110 - Add Whoosh backend with CharsetFilter.