docs: update datajoint_version to 2.1

The displayed version should indicate what the documentation covers,
not just the baseline. Since this PR documents 2.1 features (PostgreSQL),
displaying "2.1" is more accurate for users.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dimitri-yatsenko

mkdocs.yaml

@@ -214,7 +214,7 @@ markdown_extensions:
       generic: true
 extra:
   generator: false # Disable watermark
-  datajoint_version: "2.0"  # DataJoint Python version this documentation covers
+  datajoint_version: "2.1"  # DataJoint Python version this documentation covers
   social:
     - icon: main/company-logo
       link: https://www.datajoint.com