MAINT: Deprecate `parent` keyword in yaml datamodel

Summary

For #65 (closed). Deprecates the parent keyword and also fixes its functionality

Focus

As discussed in https://gitlab.com/caosdb/caosdb-advanced-user-tools/-/issues/36, a DeprecationWarning is raised when the parent keyword is seen, otherwise it now does the same as the inherit_from_obligatory keyword.

Test Environment

New unit test should be sufficient.

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