Add message about moving to linkml monorepo to README

[dalito]

This also removes the dependabot config to stop dependabot PRs in this repo.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.41%. Comparing base (f71d115) to head (5087c71).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #503   +/-   ##
=======================================
  Coverage   78.41%   78.41%           
=======================================
  Files          52       52           
  Lines        4536     4536           
  Branches      989      989           
=======================================
  Hits         3557     3557           
  Misses        764      764           
  Partials      215      215           

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