OCM: creating an invite token should return 201

[butonic]

we seem to use the wrong response code when creating an ocm invite token. I wanted to change it, but the tests say we should return a 200 Status code:

• [FAILED] [8.186 seconds]
ocm invitation workflow clients use the http endpoints exposed by sciencemesh generate the token from http apis [It] succeeds
/drone/src/tests/integration/grpc/ocm_invitation_test.go:519

  [FAILED] Expected
      <int>: 201
  to equal
      <int>: 200
  In [It] at: /drone/src/tests/integration/grpc/ocm_invitation_test.go:525 @ 09/05/24 09:17:45.026
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While I strongly disagree. I'll revert that change and rerun the CI of #4836. For now.