[OCM] Users can invite themselves to their own federated connection

[2403905]

Describe the bug

When a user generates a token for federated connection and pastes it to their own accept invitation field, then a federated connection is created with the user itself.

Related issue owncloud/ocis#11004

Expected behavior

Deny to accept the federated connection from the same instance.

Actual behavior

A clear and concise description of what happened.

Setup

Please describe how you started the server and provide a list of relevant environment variables or configuration files.

OCIS_XXX=somevalue
OCIS_YYY=somevalue
PROXY_XXX=somevalue

Additional context

Add any other context about the problem here.