Discovery endpoints refactor

[alexandrevryghem]

References

• Related to Discovery endpoints refactor  RestContract#329
• Related to Discovery endpoints refactor for more standardization and better performance DSpace#11966

Description

This PR updates the frontend to use the new endpoints from DSpace/DSpace#11966

Instructions for Reviewers

List of changes in this PR:

• Removed the ConfigurationSearchPageComponent since this component doesn't have any custom logic. The only purpose of this component was to replace the SearchConfigurationService on the MyDSpace page, but we can also achieve this by allowing the SearchConfigurationService to be configured with an injection token on the SearchComponent. This will make the theming of the SearchComponent easier, because we won't be forced to theme the ConfigurationSearchPageComponent every time as well.
• Created new services for the new endpoints & updated the model classes to reflect the returned response
• ...

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