Add views relationship schema

Problem/Motivation

When adding a Profile relationship to a View, the Config Inspector module reports missing schema definitions.
The profile module currently defines schema for views.argument_default.current_user_profile, but it does not provide schema for relationships (views.relationship.*).
As a result, Views configurations that include the profile_relationship plugin produce schema validation errors.

Steps to reproduce

1. Enable the Profile module.
2. Create a View based on users.
3. Add a relationship to a profile (Profile type: e.g., "regular_user").
4. Export the View configuration to YAML.
5. Run Config Inspector → you will see warnings about profile_type having no schema definition.

Proposed resolution

Add a schema definition for the profile_relationship Views plugin in profile/config/schema/profile.schema.yml