chore: add dune-project file

[yosefAlsuhaibani]

dune build at the root of semgrep isn't able to understand where semgrep_interfaces is coming from; this PR adds a dune-project to declare it as a package.

• I ran make setup && make to update the generated code after editing a .atd file (TODO: have a CI check)
• I made sure we're still backward compatible with old versions of the CLI.
  For example, the Semgrep backend need to still be able to consume data
  generated by Semgrep 1.50.0.
  See https://atd.readthedocs.io/en/latest/atdgen-tutorial.html#smooth-protocol-upgrades
  Note that the types related to the semgrep-core JSON output or the
  semgrep-core RPC do not need to be backward compatible!
• Any accompanying changes in semgrep-proprietary are approved and ready to merge once this PR is merged

[github-actions]

Backwards compatibility summary:

Checking backward compatibility of semgrep_output_v1.atd against past version v1.100.0
Checking backward compatibility of semgrep_output_v1.atd against past version v1.101.0
Skipping v1.102.0 because commit 1c82453e89e0b569630e48ddde015e201df0e5f9 has already been checked
Checking backward compatibility of semgrep_output_v1.atd against past version v1.103.0
Checking backward compatibility of semgrep_output_v1.atd against past version v1.104.0
Skipping v1.106.0 because commit 5e0c767ec323f3f2356d3bf8dbdf7c7836497d8a has already been checked
Skipping v1.107.0 because commit 5e0c767ec323f3f2356d3bf8dbdf7c7836497d8a has already been checked
Checking backward compatibility of semgrep_output_v1.atd against past version v1.108.0
Checking backward compatibility of semgrep_output_v1.atd against past version v1.109.0
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Skipping v1.117.0 because commit 5c6a8f569d16845ba10c27d17eeae68e481340d6 has already been checked
Checking backward compatibility of semgrep_output_v1.atd against past version v1.118.0
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Checking backward compatibility of semgrep_output_v1.atd against past version v1.125.0
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Checking backward compatibility of semgrep_output_v1.atd against past version v1.127.0
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Checking backward compatibility of semgrep_output_v1.atd against past version v1.130.0
Checking backward compatibility of semgrep_output_v1.atd against past version v1.131.0
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Checking backward compatibility of semgrep_output_v1.atd against past version v1.132.1
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Skipping v1.136.0 because commit 85c728ef38c1aef822f28035078fa2671ec7d10a has already been checked
Checking backward compatibility of semgrep_output_v1.atd against past version v1.137.0
Checking backward compatibility of semgrep_output_v1.atd against past version v1.137.1
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Checking backward compatibility of semgrep_output_v1.atd against past version v1.142.0
Checking backward compatibility of semgrep_output_v1.atd against past version v1.75.0
Skipping v1.76.0 because commit 9102031608aa4154e1c37f557550ec4eabc8780c has already been checked
Checking backward compatibility of semgrep_output_v1.atd against past version v1.77.0
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Checking backward compatibility of semgrep_output_v1.atd against past version v1.79.0
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Checking backward compatibility of semgrep_output_v1.atd against past version v1.84.0
Skipping v1.84.1 because commit 3daef49297ada205359cc1d2996354c94b628b0d has already been checked
Checking backward compatibility of semgrep_output_v1.atd against past version v1.85.0
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Checking backward compatibility of semgrep_output_v1.atd against past version v1.90.0
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