Integration tests for addEakApplication mutation (Verein360)

[seluianova]

Is your feature request related to a problem? Please describe.
Follow up for #1863

To be done:

• positive scenarios - valid requests are sent and processed
• authorization testing - api token missing / invalid
• request validation specific for Verein360 - validateAllAttributesForPreVerifiedApplication() function
• general request validation applicable to all application requests --> moved to Add tests for validation errors in the addEakApplication mutation #1932

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