[6.x] project model schema page for admins

[didoda]

This introduces a project schema page to visualize schema as svg.

Features:

• click on node to see connection and data (properties, relations, etc.)
• filter object type and see connections among nodes, relations, properties, etc.
• download project model json (beautified)
• download project model zip (split in json files beautified)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.76%. Comparing base (901c17d) to head (663899a).
⚠️ Report is 18 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1390   +/-   ##
=========================================
  Coverage     99.76%   99.76%           
- Complexity     1538     1539    +1     
=========================================
  Files           104      105    +1     
  Lines          6002     6008    +6     
=========================================
+ Hits           5988     5994    +6     
  Misses           14       14           

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