Added support for caching embedded objects without a self link & null responses

[alexandrevryghem]

References

• Fixes DSpace/DSpace#9316
• Partially solves #3163
• Fixes #2833

Description

Reduced the number of requests sent to the backend by caching embedded null objects (this will prevent unnecessary thumbnail requests). Also added support for caching embedded objects without a self-link. (Credit for this PR goes to @Atmire-Kristof)

Instructions for Reviewers

List of changes in this PR:

• Added support to cache null responses.
• Added support to cache embedded objects without self links.
• Embedded the accessStatus in places where a separate request was made.

Guidance for how to test/review this PR:

• On demo, go to your network tab and select Item Type Publication. Verify that a lot of thumbnail and accessStatus requests are made.
• Perform the same action with this fix and verify that both the thumbnail and accessStatus requests are now cached.
• These changes also apply to the browse page, the item page's related items section, the delete item tab, and the recent submissions section on the home page.

Checklist

• [x] My PR is created against the main branch of code (unless it is a backport or is fixing an issue specific to an older branch).
• [x] My PR is small in size (e.g. less than 1,000 lines of code, not including comments & specs/tests), or I have provided reasons as to why that's not possible.
• [x] My PR passes ESLint validation using npm run lint
• [x] My PR doesn't introduce circular dependencies (verified via npm run check-circ-deps)
• [x] My PR includes TypeDoc comments for all new (or modified) public methods and classes. It also includes TypeDoc for large or complex private methods.
• [x] My PR passes all specs/tests and includes new/updated specs or tests based on the Code Testing Guide.
• [x] My PR aligns with Accessibility guidelines if it makes changes to the user interface.
• [x] My PR uses i18n (internationalization) keys instead of hardcoded English text, to allow for translations.
• [x] My PR includes details on how to test it. I've provided clear instructions to reviewers on how to successfully test this fix or feature.
• [x] If my PR includes new libraries/dependencies (in package.json), I've made sure their licenses align with the DSpace BSD License based on the Licensing of Contributions documentation.
• [x] If my PR includes new features or configurations, I've provided basic technical documentation in the PR itself.
• [x] If my PR fixes an issue ticket, I've linked them together.