Reduce browse definition requests on simple item page

[KoenP]

References

• Fixes Excessive number of browse definition request on simple item page. #3700

Description

Current behavior: each ItemPageFieldComponent on a simple item page sends a request to retrieve the relevant browse definition.
New behavior: each ItemPageFieldComponent retrieves the list of all browse definitions from the cache (which has already been requested for the navbar) and searches for the relevant browse definition.

Instructions for Reviewers

List of changes in this PR

• ItemPageFieldComponent.browseDefinition modified to retrieve all browse definitions by invoking browseService.getBrowseDefinitions(), and then finding the relevant browse definition.
• BrowseDefinition and subclasses modified to have the metadataKeys field in BrowseDefinition, rather than in its subclasses.

Reproducing pre-PR behavior

Open a simple item page and observe that that several requests are being made to /server/api/discover/browses/search/byFields.

Testing the PR

Open a simple item page and observe that only one request is made to /server/api/discover/browses, and that the behavior of the page is otherwise unchanged.

Checklist

• 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).
• 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.
• My PR passes ESLint validation using npm run lint
• My PR doesn't introduce circular dependencies (verified via npm run check-circ-deps)
• My PR includes TypeDoc comments for all new (or modified) public methods and classes. It also includes TypeDoc for large or complex private methods.
• My PR passes all specs/tests and includes new/updated specs or tests based on the Code Testing Guide.
• My PR aligns with Accessibility guidelines if it makes changes to the user interface.
• My PR uses i18n (internationalization) keys instead of hardcoded English text, to allow for translations.
• 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.
• 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.
• If my PR includes new features or configurations, I've provided basic technical documentation in the PR itself.
• If my PR fixes an issue ticket, I've linked them together.