add Dfns as an integration tooling and service provider

[djin-dfns]

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[cla-idx-bot]

Dear @djin-dfns,

In order to potentially merge your code in this open-source repository and therefore proceed with your contribution, we need to have your approval on DFINITY's CLA.

If you decide to agree with it, please visit this issue and read the instructions there. Once you have signed it, re-trigger the workflow on this PR to see if your code can be merged.

— The DFINITY Foundation